🏷

Classifications

Harrison's Chapter

ICD-O Morphology

◆

Subtypes

2

Anal Canal Squamous Cell Carcinoma NCIT:C7469

The dominant histologic type, accounting for the large majority of anal canal cancers. Arises from the stratified squamous epithelium of the anal canal and is strongly associated with high-risk HPV infection, predominantly HPV-16.

Show evidence (1 reference)

PMID:42101137 SUPPORT Human Clinical

"All specimens contained a single HPV genotype: 93.3% HPV16, 3.3% HPV18, and 3.3% HPV31."

Laser-capture microdissection of anal squamous cell carcinoma lesions from women attributed HPV-16 as the causal genotype in nearly all cases, supporting HPV-16-driven anal SCC as the dominant subtype.

Anal Canal Adenocarcinoma NCIT:C7471

A rare histologic subtype arising from glandular epithelium of the anal canal or from anal glands. Generally not HPV-associated and treated more similarly to rectal adenocarcinoma.

Show evidence (1 reference)

PMID:41452529 SUPPORT Human Clinical

"In Japan, adenocarcinoma accounted for 66.8-75.5% of the ACC cases, while SCC represented only 16.2-24.4%, in contrast to the 70-85% SCC predominance reported in Western countries."

Japanese and Western registry data document that anal canal adenocarcinoma is a distinct, less common histologic subtype of anal canal carcinoma; the histologic distribution varies by population, with SCC predominant in Western series.

⚙

Pathophysiology

6

HPV Infection of Anal Squamous Epithelium

High-risk HPV (predominantly HPV-16) infects basal stratified squamous epithelial cells of the anal canal, typically at the anal transformation zone where squamous and columnar epithelia meet. Persistent infection over years to decades is the necessary first step in HPV-driven anal carcinogenesis.

stratified squamous epithelial cell of anal canal link

anal canal link

Downstream

E6 Oncoprotein-Mediated p53 Degradation Persistent HPV infection enables sustained E6 expression

E7 Oncoprotein-Mediated pRB Inactivation Persistent HPV infection enables sustained E7 expression

Show evidence (1 reference)

PMID:41452529 SUPPORT Human Clinical

"HPV was positive in 85% of the SCC cases, with HPV-16 as the most prevalent genotype"

Registry data document a high HPV prevalence in anal canal SCC with HPV-16 as the most common genotype, supporting HPV infection of anal squamous epithelium as the upstream pathophysiologic step.

E6 Oncoprotein-Mediated p53 Degradation

The HPV E6 oncoprotein binds to the cellular E3 ubiquitin ligase E6AP and targets p53 for proteasomal degradation. Loss of p53 function eliminates DNA damage checkpoints and apoptotic responses in infected anal squamous epithelial cells.

stratified squamous epithelial cell of anal canal link

proteasome-mediated ubiquitin-dependent protein catabolic process link ↑ INCREASED apoptotic process link ↓ DECREASED

Downstream

Genomic Instability p53 loss permits cells with damaged DNA to survive and proliferate

Show evidence (2 references)

PMID:2175676 SUPPORT In Vitro

"the E6 proteins of the oncogenic HPVs"

Classic biochemical evidence that HPV E6 from oncogenic types stimulates degradation of p53, supporting E6-mediated p53 loss as a shared mechanism in HPV-driven anogenital cancers including anal squamous cell carcinoma.

PMID:2175676 SUPPORT In Vitro

"p53 is ATP dependent and involves the ubiquitin-dependent protease system."

E6-promoted p53 degradation occurs via the ubiquitin-proteasome system, providing direct mechanistic support for proteasomal destruction of p53 in HPV-infected squamous epithelium.

E7 Oncoprotein-Mediated pRB Inactivation

The HPV E7 oncoprotein binds to and inactivates the retinoblastoma protein (pRB), releasing E2F transcription factors and driving uncontrolled cell cycle progression in anal squamous epithelial cells.

stratified squamous epithelial cell of anal canal link

G1/S transition of mitotic cell cycle link ⚠ ABNORMAL cell population proliferation link ↑ INCREASED

Downstream

Genomic Instability Unrestrained proliferation in the setting of impaired checkpoints

Show evidence (1 reference)

PMID:2537532 SUPPORT In Vitro

"the E7 oncoprotein of the human papilloma virus type-16 can"

Classic biochemical evidence that HPV-16 E7 binds the retinoblastoma gene product, supporting E7-mediated pRB inactivation as the shared mechanism driving uncontrolled S-phase entry in HPV-driven anogenital carcinomas, including anal squamous cell carcinoma.

Genomic Instability

Combined loss of p53 and pRB function, along with HPV-associated chromosomal aberrations, drives accumulation of genetic alterations and progression from anal intraepithelial neoplasia to invasive squamous cell carcinoma.

DNA damage response link ⚠ ABNORMAL

Downstream

Anal Intraepithelial Neoplasia Progression Genomic alterations drive progression from AIN to invasive carcinoma

Show evidence (1 reference)

PMID:34790403 SUPPORT Human Clinical

"The most frequently mutated genes included PIK3CA (28.1%), KMT2D (19.5%), FBXW7 (12%), TP53 (12%) and PTEN (10.8%)."

Multiplatform molecular profiling of 311 anal squamous cell carcinomas identifies recurrent somatic mutations across PIK3CA, KMT2D, FBXW7, TP53, and PTEN, supporting genomic instability and accumulation of driver alterations during anal squamous cell carcinogenesis.

Anal Intraepithelial Neoplasia Progression

HPV-driven dysplasia of the anal squamous epithelium progresses through a spectrum of anal intraepithelial neoplasia (AIN1, AIN2, AIN3 / high-grade squamous intraepithelial lesion) to invasive anal squamous cell carcinoma. High-grade lesions carry a significant risk of progression, particularly in immunosuppressed patients.

stratified squamous epithelial cell of anal canal link

cell population proliferation link ↑ INCREASED

Downstream

Adaptive Immune Resistance Invasive HPV-driven anal squamous cell carcinoma upregulates PD-L1 and engages adaptive immune resistance to evade anti-tumor T cell responses.

Show evidence (1 reference)

PMID:40019005 SUPPORT Human Clinical

"the benefits of treating precancerous anal lesions to reduce the risk of progression to anal SCC"

Systematic review of anal cancer screening recommendations supports the AIN-to-invasive-SCC progression pathway as the rationale for treating high-grade precancerous anal lesions in high-risk groups.

Adaptive Immune Resistance

Anal squamous cell carcinoma cells frequently express PD-L1 and PD-1 is expressed on tumor-infiltrating T cells, consistent with adaptive immune resistance to anti-tumor immunity. This mechanism is the therapeutic rationale for PD-1 blockade (pembrolizumab, nivolumab) in recurrent or metastatic disease.

stratified squamous epithelial cell of anal canal link

Negative Regulation of T Cell Mediated Immunity link ↑ INCREASED

Show evidence (1 reference)

PMID:34790403 SUPPORT Human Clinical

"The expression of PD-1 was seen in 68.8% and PD-L1 in 40.5% of tumors."

Multiplatform profiling of 311 anal squamous cell carcinomas documents PD-L1 expression in 40.5% of tumors and PD-1 expression on infiltrating cells in 68.8%, supporting adaptive immune resistance as an active mechanism in anal squamous cell carcinoma and providing the rationale for PD-1 checkpoint blockade.

✶

Histopathology

2

Anal Canal Squamous Cell Carcinoma VERY_FREQUENT

Squamous cell carcinoma is the dominant histologic type of anal canal carcinoma.

Show evidence (1 reference)

PMID:41452529 SUPPORT Human Clinical

"70-85% SCC predominance reported in Western countries"

Western registry data confirm squamous cell carcinoma as the predominant histologic type of anal canal carcinoma.

Anal Canal Adenocarcinoma OCCASIONAL

Adenocarcinoma arising from glandular epithelium of the anal canal is much less common than squamous cell carcinoma.

Show evidence (1 reference)

PMID:41452529 SUPPORT Human Clinical

"In Japan, adenocarcinoma accounted for 66.8-75.5% of the ACC cases, while SCC represented only 16.2-24.4%"

Adenocarcinoma is a recognized histologic subtype of anal canal carcinoma, with frequency varying by population.

⬡

Pathograph

Use the checkboxes to hide or show graph categories. Hover nodes for evidence and cross-linked metadata.

●

Phenotypes

4

Blood 1

Rectal Bleeding Hematochezia (HP:0002573)

Show evidence (1 reference)

PMID:33085290 SUPPORT Human Clinical

"Hematochezia is the passage of frank blood per rectum"

Reference clinical definition of hematochezia as bright red bleeding per rectum, which is the most common presenting symptom of anal canal cancer.

Other 3

Anal Pain Anal pain (HP:0500005)

Show evidence (1 reference)

PMID:37731305 SUPPORT Human Clinical

"Patients diagnosed with both cancers often experience multiple symptoms including pain, constipation, nausea, and vomiting."

Palliative care review of colorectal and anal malignancies supports pain as a common symptom experienced by patients with anal cancer.

Anal Canal Squamous Carcinoma Anal canal squamous carcinoma (HP:0006763)

Show evidence (1 reference)

PMID:34790403 SUPPORT Human Clinical

"Squamous cell carcinoma of the anal canal (SCCA) is an uncommon malignancy with limited therapeutic options."

Supports anal canal squamous cell carcinoma as the defining neoplastic entity of HPV-associated anal canal cancer.

Inguinal Lymphadenopathy Inguinal lymphadenopathy (HP:0034751)

Show evidence (1 reference)

PMID:39882228 SUPPORT Human Clinical

"Primary tumor progression was associated with metastasis and recurrence of the inguinal node"

Multicenter cohort of 435 patients with anal canal squamous cell carcinoma supports inguinal lymph node metastasis as a key pattern of regional spread, consistent with the lymphatic drainage of the anal canal below the dentate line.

🧬

Genetic Associations

2

TP53 (Inactivated by E6 Oncoprotein)

Show evidence (1 reference)

PMID:34790403 SUPPORT Human Clinical

"Human papillomavirus (HPV)-negative tumors are frequently TP53-mutated (TP53-MT) and often resistant to therapy."

Multiplatform profiling of 311 anal SCC specimens supports the pattern of TP53 mutation enrichment in HPV-negative anal squamous cell carcinoma, distinct from the HPV-driven E6-mediated p53 degradation seen in HPV-positive disease.

PIK3CA (Somatic Mutations)

Show evidence (1 reference)

PMID:34790403 SUPPORT Human Clinical

"The most frequently mutated genes included PIK3CA (28.1%)"

Large molecular profiling cohort supports PIK3CA as the most frequently mutated gene in anal canal squamous cell carcinoma.

💊

Treatments

4

HPV Vaccination

Action: vaccination MAXO:0001017

Prophylactic vaccination against high-risk HPV types prevents anogenital HPV infection and reduces the incidence of anal high-grade squamous intraepithelial lesions and anal cancer. Most effective when given before HPV exposure.

Show evidence (1 reference)

PMID:42101137 SUPPORT Human Clinical

"All cases in this sample could potentially have been prevented by nonavalent prophylactic vaccination, and 97% by the quadrivalent vaccine."

Lesion-specific HPV genotyping of anal squamous cell carcinomas in women indicates that nonavalent (and largely quadrivalent) HPV vaccination could prevent the great majority of HPV-driven anal cancers, supporting HPV vaccination as primary prevention.

Chemoradiation (Nigro regimen)

Action: radiation therapy MAXO:0000014

Agent: 5-fluorouracil ↗ mitomycin C ↗

Concurrent 5-fluorouracil and mitomycin-C with external-beam radiation therapy is the standard curative treatment for localized anal canal squamous cell carcinoma, preserving anal sphincter function and avoiding upfront abdominoperineal resection.

Show evidence (2 references)

PMID:15571466 SUPPORT Human Clinical

"Since the original contribution by Nigro in 1974, surprisingly few changes have been made to the standard of care in chemotherapy, which still consists of a combination of 5-fluorouracil and mitomycin C."

Establishes 5-fluorouracil plus mitomycin C combined with radiation (the Nigro regimen) as the long-standing standard chemoradiation backbone for anal canal cancer.

PMID:41452529 SUPPORT Human Clinical

"The adoption of chemoradiotherapy (CRT) increased from 14% in the 1990 s to over 80% after 2010, achieving survival outcomes comparable to surgery."

Registry data document the shift from primary surgery to chemoradiation as the dominant curative treatment for anal canal carcinoma, supporting its role as standard curative therapy.

Salvage Abdominoperineal Resection

Action: surgical procedure MAXO:0000004

Surgical removal of the anus, rectum, and surrounding tissues with permanent colostomy is reserved for residual or recurrent anal canal carcinoma after definitive chemoradiation.

Show evidence (1 reference)

PMID:37210274 SUPPORT Human Clinical

"The primary treatment for locoregional failure following chemoradiotherapy for squamous cell carcinoma of the anus (SCCA) is salvage abdominoperineal resection (APR)."

Multicenter retrospective cohort supports salvage abdominoperineal resection as the standard treatment for locoregional failure after definitive chemoradiation for anal squamous cell carcinoma.

Immune Checkpoint Inhibitor Therapy

Action: immunotherapy Ontology label: Immunotherapy NCIT:C15262

Agent: pembrolizumab ↗

PD-1 inhibitors such as pembrolizumab and nivolumab have demonstrated activity in recurrent or metastatic anal canal squamous cell carcinoma and are used in the second-line and beyond setting.

Mechanism Target:

INHIBITS Adaptive Immune Resistance — PD-1 blockade with pembrolizumab counteracts adaptive immune resistance by interrupting PD-1/PD-L1 signaling between tumor-infiltrating T cells and PD-L1-expressing anal squamous cell carcinoma cells, restoring anti-tumor T cell activity.

Show evidence (1 reference)

PMID:35114169 SUPPORT Human Clinical

"Pembrolizumab monotherapy is a possible treatment option with a favourable benefit-risk ratio for patients with previously treated advanced anal squamous cell carcinoma who have no alternative satisfactory treatment options."

Clinical activity of pembrolizumab in advanced anal squamous cell carcinoma supports targeting PD-1-mediated adaptive immune resistance as a therapeutically relevant mechanism.

Show evidence (1 reference)

PMID:35114169 SUPPORT Human Clinical

"Pembrolizumab monotherapy is a possible treatment option with a favourable benefit-risk ratio for patients with previously treated advanced anal squamous cell carcinoma who have no alternative satisfactory treatment options."

Phase 2 KEYNOTE-158 cohort supports pembrolizumab as an active second-line treatment for advanced anal squamous cell carcinoma.

🌍

Environmental Factors

3

Human Papillomavirus Infection

Persistent infection with high-risk HPV, particularly HPV-16, is the necessary causal exposure for the great majority of anal canal squamous cell carcinomas.

Show evidence (1 reference)

PMID:42101137 SUPPORT Human Clinical

"Anal cancer, caused by persistent infection with oncogenic human papillomavirus (HPV), is rare in the general population."

Supports persistent oncogenic HPV infection as the necessary causal environmental exposure for anal cancer.

HIV Infection / Immunosuppression

HIV infection and other forms of chronic immunosuppression (including iatrogenic immunosuppression in solid organ transplant recipients) markedly increase the risk of HPV-associated anal cancer, with the highest incidence in men who have sex with men living with HIV.

Show evidence (1 reference)

PMID:42101137 SUPPORT Human Clinical

"certain groups, such as men who have sex with men living with HIV, are at much higher risk"

Supports HIV infection (particularly in MSM) as a major risk modifier for anal cancer.

Tobacco Smoking

Cigarette smoking is an established risk factor for anal canal squamous cell carcinoma, independent of HPV exposure.

Show evidence (1 reference)

PMID:15241823 SUPPORT Human Clinical

"Current smokers among men and women were at particularly high risk for anal cancer, independent of age and other risk factors"

Population-based case-control study supports current cigarette smoking as an independent risk factor for anal cancer in both men and women, independent of HPV-related sexual exposures.

🔬

Biochemical Markers

2

HPV DNA Testing

p16 Immunohistochemistry

{ }

Source YAML

click to show

name: Anal Canal Carcinoma
creation_date: '2026-05-13T23:05:20Z'
updated_date: '2026-05-14T06:01:07Z'
description: >-
  Anal canal carcinoma is a malignancy arising from the epithelium of the anal
  canal, with the vast majority being squamous cell carcinoma caused by
  persistent infection with high-risk human papillomavirus (HPV), most commonly
  HPV-16. The viral oncoproteins E6 and E7 drive carcinogenesis by inactivating
  the tumor suppressors p53 and pRB, respectively, in stratified squamous
  epithelial cells of the anal canal. Incidence is markedly increased in
  people living with HIV, particularly men who have sex with men, and in other
  immunosuppressed populations. Combined chemoradiation (the Nigro regimen of
  5-fluorouracil and mitomycin with external-beam radiation) is the standard
  curative treatment for localized disease, with salvage abdominoperineal
  resection reserved for residual or recurrent disease. Immune checkpoint
  inhibitors targeting PD-1 (pembrolizumab, nivolumab) have activity in
  recurrent or metastatic disease.
categories:
- Gastrointestinal Malignancy
- Viral-Associated Cancer
- HPV-Related Cancer
parents:
- anal carcinoma
has_subtypes:
- name: Anal Canal Squamous Cell Carcinoma
  subtype_term:
    preferred_term: Anal Canal Squamous Cell Carcinoma
    term:
      id: NCIT:C7469
      label: Anal Canal Squamous Cell Carcinoma
  description: >-
    The dominant histologic type, accounting for the large majority of anal
    canal cancers. Arises from the stratified squamous epithelium of the anal
    canal and is strongly associated with high-risk HPV infection,
    predominantly HPV-16.
  evidence:
  - reference: PMID:42101137
    reference_title: "Causative Human Papillomavirus (HPV) Genotypes of Anal Cancers in Australian Cisgender Women."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "All specimens contained a single HPV genotype: 93.3% HPV16, 3.3% HPV18, and 3.3% HPV31."
    explanation: >-
      Laser-capture microdissection of anal squamous cell carcinoma lesions
      from women attributed HPV-16 as the causal genotype in nearly all
      cases, supporting HPV-16-driven anal SCC as the dominant subtype.
- name: Anal Canal Adenocarcinoma
  subtype_term:
    preferred_term: Anal Canal Adenocarcinoma
    term:
      id: NCIT:C7471
      label: Anal Canal Adenocarcinoma
  description: >-
    A rare histologic subtype arising from glandular epithelium of the anal
    canal or from anal glands. Generally not HPV-associated and treated more
    similarly to rectal adenocarcinoma.
  evidence:
  - reference: PMID:41452529
    reference_title: "Cancer epidemiology in rare and hereditary colorectal diseases 2) anal canal cancer (cancer statistics)."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In Japan, adenocarcinoma accounted for 66.8-75.5% of the ACC cases, while SCC represented only 16.2-24.4%, in contrast to the 70-85% SCC predominance reported in Western countries."
    explanation: >-
      Japanese and Western registry data document that anal canal
      adenocarcinoma is a distinct, less common histologic subtype of
      anal canal carcinoma; the histologic distribution varies by
      population, with SCC predominant in Western series.
infectious_agent:
- name: Human Papillomavirus (HPV)
  description: >-
    High-risk HPV types, particularly HPV-16, cause the great majority of anal
    squamous cell carcinomas. Persistent infection with high-risk HPV in anal
    canal stratified squamous epithelium is the necessary causal exposure for
    HPV-associated anal carcinogenesis.
  evidence:
  - reference: PMID:42101137
    reference_title: "Causative Human Papillomavirus (HPV) Genotypes of Anal Cancers in Australian Cisgender Women."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Anal cancer, caused by persistent infection with oncogenic human papillomavirus (HPV), is rare in the general population."
    explanation: >-
      Supports persistent oncogenic HPV infection as the necessary causal
      agent for anal cancer.
  infectious_agent_term:
    preferred_term: Human papillomavirus 16
    term:
      id: NCBITaxon:333760
      label: Human papillomavirus 16
environmental:
- name: Human Papillomavirus Infection
  description: >-
    Persistent infection with high-risk HPV, particularly HPV-16, is the
    necessary causal exposure for the great majority of anal canal squamous
    cell carcinomas.
  effect: CAUSAL
  evidence:
  - reference: PMID:42101137
    reference_title: "Causative Human Papillomavirus (HPV) Genotypes of Anal Cancers in Australian Cisgender Women."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Anal cancer, caused by persistent infection with oncogenic human papillomavirus (HPV), is rare in the general population."
    explanation: >-
      Supports persistent oncogenic HPV infection as the necessary causal
      environmental exposure for anal cancer.
- name: HIV Infection / Immunosuppression
  description: >-
    HIV infection and other forms of chronic immunosuppression (including
    iatrogenic immunosuppression in solid organ transplant recipients)
    markedly increase the risk of HPV-associated anal cancer, with the
    highest incidence in men who have sex with men living with HIV.
  effect: HARMFUL
  evidence:
  - reference: PMID:42101137
    reference_title: "Causative Human Papillomavirus (HPV) Genotypes of Anal Cancers in Australian Cisgender Women."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "certain groups, such as men who have sex with men living with HIV, are at much higher risk"
    explanation: >-
      Supports HIV infection (particularly in MSM) as a major risk
      modifier for anal cancer.
- name: Tobacco Smoking
  description: >-
    Cigarette smoking is an established risk factor for anal canal squamous
    cell carcinoma, independent of HPV exposure.
  effect: HARMFUL
  evidence:
  - reference: PMID:15241823
    reference_title: "Human papillomavirus, smoking, and sexual practices in the etiology of anal cancer."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Current smokers among men and women were at particularly high risk for anal cancer, independent of age and other risk factors"
    explanation: >-
      Population-based case-control study supports current cigarette smoking
      as an independent risk factor for anal cancer in both men and women,
      independent of HPV-related sexual exposures.
pathophysiology:
- name: HPV Infection of Anal Squamous Epithelium
  description: >-
    High-risk HPV (predominantly HPV-16) infects basal stratified squamous
    epithelial cells of the anal canal, typically at the anal transformation
    zone where squamous and columnar epithelia meet. Persistent infection
    over years to decades is the necessary first step in HPV-driven anal
    carcinogenesis.
  cell_types:
  - preferred_term: stratified squamous epithelial cell of anal canal
    term:
      id: CL:0009066
      label: stratified squamous epithelial cell of anal canal
  locations:
  - preferred_term: anal canal
    term:
      id: UBERON:0000159
      label: anal canal
  evidence:
  - reference: PMID:41452529
    reference_title: "Cancer epidemiology in rare and hereditary colorectal diseases 2) anal canal cancer (cancer statistics)."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "HPV was positive in 85% of the SCC cases, with HPV-16 as the most prevalent genotype"
    explanation: >-
      Registry data document a high HPV prevalence in anal canal SCC with
      HPV-16 as the most common genotype, supporting HPV infection of anal
      squamous epithelium as the upstream pathophysiologic step.
  downstream:
  - target: E6 Oncoprotein-Mediated p53 Degradation
    description: Persistent HPV infection enables sustained E6 expression
  - target: E7 Oncoprotein-Mediated pRB Inactivation
    description: Persistent HPV infection enables sustained E7 expression
- name: E6 Oncoprotein-Mediated p53 Degradation
  description: >-
    The HPV E6 oncoprotein binds to the cellular E3 ubiquitin ligase E6AP and
    targets p53 for proteasomal degradation. Loss of p53 function eliminates
    DNA damage checkpoints and apoptotic responses in infected anal squamous
    epithelial cells.
  cell_types:
  - preferred_term: stratified squamous epithelial cell of anal canal
    term:
      id: CL:0009066
      label: stratified squamous epithelial cell of anal canal
  biological_processes:
  - preferred_term: proteasome-mediated ubiquitin-dependent protein catabolic process
    modifier: INCREASED
    term:
      id: GO:0043161
      label: proteasome-mediated ubiquitin-dependent protein catabolic process
  - preferred_term: apoptotic process
    modifier: DECREASED
    term:
      id: GO:0006915
      label: apoptotic process
  evidence:
  - reference: PMID:2175676
    reference_title: "The E6 oncoprotein encoded by human papillomavirus types 16 and 18 promotes the degradation of p53."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "the E6 proteins of the oncogenic HPVs"
    explanation: >-
      Classic biochemical evidence that HPV E6 from oncogenic types
      stimulates degradation of p53, supporting E6-mediated p53 loss as a
      shared mechanism in HPV-driven anogenital cancers including anal
      squamous cell carcinoma.
  - reference: PMID:2175676
    reference_title: "The E6 oncoprotein encoded by human papillomavirus types 16 and 18 promotes the degradation of p53."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "p53 is ATP dependent and involves the ubiquitin-dependent protease system."
    explanation: >-
      E6-promoted p53 degradation occurs via the ubiquitin-proteasome
      system, providing direct mechanistic support for proteasomal
      destruction of p53 in HPV-infected squamous epithelium.
  downstream:
  - target: Genomic Instability
    description: p53 loss permits cells with damaged DNA to survive and proliferate
- name: E7 Oncoprotein-Mediated pRB Inactivation
  description: >-
    The HPV E7 oncoprotein binds to and inactivates the retinoblastoma
    protein (pRB), releasing E2F transcription factors and driving
    uncontrolled cell cycle progression in anal squamous epithelial cells.
  cell_types:
  - preferred_term: stratified squamous epithelial cell of anal canal
    term:
      id: CL:0009066
      label: stratified squamous epithelial cell of anal canal
  biological_processes:
  - preferred_term: G1/S transition of mitotic cell cycle
    modifier: ABNORMAL
    term:
      id: GO:0000082
      label: G1/S transition of mitotic cell cycle
  - preferred_term: cell population proliferation
    modifier: INCREASED
    term:
      id: GO:0008283
      label: cell population proliferation
  evidence:
  - reference: PMID:2537532
    reference_title: "The human papilloma virus-16 E7 oncoprotein is able to bind to the retinoblastoma gene product."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "the E7 oncoprotein of the human papilloma virus type-16 can"
    explanation: >-
      Classic biochemical evidence that HPV-16 E7 binds the retinoblastoma
      gene product, supporting E7-mediated pRB inactivation as the shared
      mechanism driving uncontrolled S-phase entry in HPV-driven anogenital
      carcinomas, including anal squamous cell carcinoma.
  downstream:
  - target: Genomic Instability
    description: Unrestrained proliferation in the setting of impaired checkpoints
- name: Genomic Instability
  description: >-
    Combined loss of p53 and pRB function, along with HPV-associated
    chromosomal aberrations, drives accumulation of genetic alterations and
    progression from anal intraepithelial neoplasia to invasive squamous
    cell carcinoma.
  biological_processes:
  - preferred_term: DNA damage response
    modifier: ABNORMAL
    term:
      id: GO:0006974
      label: DNA damage response
  evidence:
  - reference: PMID:34790403
    reference_title: "Molecular characterization of squamous cell carcinoma of the anal canal."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The most frequently mutated genes included PIK3CA (28.1%), KMT2D (19.5%), FBXW7 (12%), TP53 (12%) and PTEN (10.8%)."
    explanation: >-
      Multiplatform molecular profiling of 311 anal squamous cell
      carcinomas identifies recurrent somatic mutations across
      PIK3CA, KMT2D, FBXW7, TP53, and PTEN, supporting genomic
      instability and accumulation of driver alterations during anal
      squamous cell carcinogenesis.
  downstream:
  - target: Anal Intraepithelial Neoplasia Progression
    description: Genomic alterations drive progression from AIN to invasive carcinoma
- name: Anal Intraepithelial Neoplasia Progression
  description: >-
    HPV-driven dysplasia of the anal squamous epithelium progresses through
    a spectrum of anal intraepithelial neoplasia (AIN1, AIN2, AIN3 / high-grade
    squamous intraepithelial lesion) to invasive anal squamous cell
    carcinoma. High-grade lesions carry a significant risk of progression,
    particularly in immunosuppressed patients.
  cell_types:
  - preferred_term: stratified squamous epithelial cell of anal canal
    term:
      id: CL:0009066
      label: stratified squamous epithelial cell of anal canal
  biological_processes:
  - preferred_term: cell population proliferation
    modifier: INCREASED
    term:
      id: GO:0008283
      label: cell population proliferation
  evidence:
  - reference: PMID:40019005
    reference_title: "Recent Guidelines on Anal Cancer Screening: A Systematic Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "the benefits of treating precancerous anal lesions to reduce the risk of progression to anal SCC"
    explanation: >-
      Systematic review of anal cancer screening recommendations supports
      the AIN-to-invasive-SCC progression pathway as the rationale for
      treating high-grade precancerous anal lesions in high-risk groups.
  downstream:
  - target: Adaptive Immune Resistance
    description: >-
      Invasive HPV-driven anal squamous cell carcinoma upregulates PD-L1
      and engages adaptive immune resistance to evade anti-tumor T cell
      responses.
- name: Adaptive Immune Resistance
  conforms_to: "immune_checkpoint_blockade#Adaptive Immune Resistance"
  description: >-
    Anal squamous cell carcinoma cells frequently express PD-L1 and PD-1
    is expressed on tumor-infiltrating T cells, consistent with adaptive
    immune resistance to anti-tumor immunity. This mechanism is the
    therapeutic rationale for PD-1 blockade (pembrolizumab, nivolumab)
    in recurrent or metastatic disease.
  cell_types:
  - preferred_term: stratified squamous epithelial cell of anal canal
    term:
      id: CL:0009066
      label: stratified squamous epithelial cell of anal canal
  biological_processes:
  - preferred_term: Negative Regulation of T Cell Mediated Immunity
    modifier: INCREASED
    term:
      id: GO:0002710
      label: negative regulation of T cell mediated immunity
  evidence:
  - reference: PMID:34790403
    reference_title: "Molecular characterization of squamous cell carcinoma of the anal canal."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The expression of PD-1 was seen in 68.8% and PD-L1 in 40.5% of tumors."
    explanation: >-
      Multiplatform profiling of 311 anal squamous cell carcinomas
      documents PD-L1 expression in 40.5% of tumors and PD-1 expression
      on infiltrating cells in 68.8%, supporting adaptive immune
      resistance as an active mechanism in anal squamous cell carcinoma
      and providing the rationale for PD-1 checkpoint blockade.
histopathology:
- name: Anal Canal Squamous Cell Carcinoma
  finding_term:
    preferred_term: Anal Canal Squamous Cell Carcinoma
    term:
      id: NCIT:C7469
      label: Anal Canal Squamous Cell Carcinoma
  frequency: VERY_FREQUENT
  description: >-
    Squamous cell carcinoma is the dominant histologic type of anal canal
    carcinoma.
  evidence:
  - reference: PMID:41452529
    reference_title: "Cancer epidemiology in rare and hereditary colorectal diseases 2) anal canal cancer (cancer statistics)."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "70-85% SCC predominance reported in Western countries"
    explanation: >-
      Western registry data confirm squamous cell carcinoma as the
      predominant histologic type of anal canal carcinoma.
- name: Anal Canal Adenocarcinoma
  finding_term:
    preferred_term: Anal Canal Adenocarcinoma
    term:
      id: NCIT:C7471
      label: Anal Canal Adenocarcinoma
  frequency: OCCASIONAL
  description: >-
    Adenocarcinoma arising from glandular epithelium of the anal canal is
    much less common than squamous cell carcinoma.
  evidence:
  - reference: PMID:41452529
    reference_title: "Cancer epidemiology in rare and hereditary colorectal diseases 2) anal canal cancer (cancer statistics)."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In Japan, adenocarcinoma accounted for 66.8-75.5% of the ACC cases, while SCC represented only 16.2-24.4%"
    explanation: >-
      Adenocarcinoma is a recognized histologic subtype of anal canal
      carcinoma, with frequency varying by population.
phenotypes:
- category: Gastrointestinal
  name: Rectal Bleeding
  diagnostic: true
  description: >-
    Bright red bleeding per rectum is the most common presenting symptom of
    anal canal cancer and frequently prompts initial evaluation.
  phenotype_term:
    preferred_term: Hematochezia
    term:
      id: HP:0002573
      label: Hematochezia
  evidence:
  - reference: PMID:33085290
    reference_title: "Rectal Bleeding."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Hematochezia is the passage of frank blood per rectum"
    explanation: >-
      Reference clinical definition of hematochezia as bright red bleeding
      per rectum, which is the most common presenting symptom of anal
      canal cancer.
- category: Gastrointestinal
  name: Anal Pain
  description: >-
    Pain is among the multiple symptoms commonly experienced by patients
    with anal canal cancer over the course of their disease, as documented
    in palliative care studies of colorectal and anal malignancies.
  phenotype_term:
    preferred_term: Anal pain
    term:
      id: HP:0500005
      label: Anal pain
  evidence:
  - reference: PMID:37731305
    reference_title: "Palliative care in colorectal and anal malignancies from diagnosis to death."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Patients diagnosed with both cancers often experience multiple symptoms including pain, constipation, nausea, and vomiting."
    explanation: >-
      Palliative care review of colorectal and anal malignancies supports
      pain as a common symptom experienced by patients with anal cancer.
- category: Neoplastic
  name: Anal Canal Squamous Carcinoma
  diagnostic: true
  description: >-
    Invasive squamous cell carcinoma of the anal canal is the defining
    histopathologic feature of HPV-associated anal canal cancer.
  phenotype_term:
    preferred_term: Anal canal squamous carcinoma
    term:
      id: HP:0006763
      label: Anal canal squamous carcinoma
  evidence:
  - reference: PMID:34790403
    reference_title: "Molecular characterization of squamous cell carcinoma of the anal canal."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Squamous cell carcinoma of the anal canal (SCCA) is an uncommon malignancy with limited therapeutic options."
    explanation: >-
      Supports anal canal squamous cell carcinoma as the defining
      neoplastic entity of HPV-associated anal canal cancer.
- category: Lymphatic
  name: Inguinal Lymphadenopathy
  description: >-
    Anal canal cancer below the dentate line drains preferentially to
    inguinal lymph nodes; palpable inguinal lymphadenopathy may indicate
    regional metastatic involvement.
  phenotype_term:
    preferred_term: Inguinal lymphadenopathy
    term:
      id: HP:0034751
      label: Inguinal lymphadenopathy
  evidence:
  - reference: PMID:39882228
    reference_title: "Metastatic Status and Dissection Effect of Regional/Extraregional Lymph Nodes in Japanese Patients with Squamous Cell Carcinoma of the Anal Canal: A Multicenter Retrospective Cohort Study."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Primary tumor progression was associated with metastasis and recurrence of the inguinal node"
    explanation: >-
      Multicenter cohort of 435 patients with anal canal squamous cell
      carcinoma supports inguinal lymph node metastasis as a key pattern
      of regional spread, consistent with the lymphatic drainage of the
      anal canal below the dentate line.
biochemical:
- name: HPV DNA Testing
  notes: >-
    Detection of high-risk HPV DNA by PCR or hybrid capture in anal
    cytology or biopsy specimens supports an HPV-associated etiology and
    is used in high-risk screening programs.
- name: p16 Immunohistochemistry
  notes: >-
    Diffuse block-positive p16INK4a immunostaining is a surrogate marker of
    transcriptionally active high-risk HPV E7 in anal squamous lesions and
    supports the diagnosis of HPV-associated anal squamous neoplasia.
genetic:
- name: TP53
  association: Inactivated by E6 Oncoprotein
  notes: >-
    In HPV-positive anal squamous cell carcinoma, p53 function is lost
    through E6-mediated degradation rather than somatic TP53 mutation.
    Rare HPV-negative anal cancers may harbor TP53 mutations.
  evidence:
  - reference: PMID:34790403
    reference_title: "Molecular characterization of squamous cell carcinoma of the anal canal."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Human papillomavirus (HPV)-negative tumors are frequently TP53-mutated (TP53-MT) and often resistant to therapy."
    explanation: >-
      Multiplatform profiling of 311 anal SCC specimens supports the
      pattern of TP53 mutation enrichment in HPV-negative anal squamous
      cell carcinoma, distinct from the HPV-driven E6-mediated p53
      degradation seen in HPV-positive disease.
- name: PIK3CA
  association: Somatic Mutations
  notes: >-
    Somatic PIK3CA mutations occur in approximately a quarter of anal
    squamous cell carcinomas and may represent a therapeutic target via
    PI3K/AKT/mTOR signaling.
  evidence:
  - reference: PMID:34790403
    reference_title: "Molecular characterization of squamous cell carcinoma of the anal canal."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The most frequently mutated genes included PIK3CA (28.1%)"
    explanation: >-
      Large molecular profiling cohort supports PIK3CA as the most
      frequently mutated gene in anal canal squamous cell carcinoma.
diagnosis:
- name: Histopathologic confirmation of anal canal malignancy
  description: >-
    Tissue diagnosis via anoscopy-guided biopsy is required to confirm
    invasive carcinoma and classify histology (squamous cell carcinoma vs
    adenocarcinoma), which determines treatment planning.
  diagnosis_term:
    preferred_term: clinical assessment
    term:
      id: MAXO:0000487
      label: clinical assessment
  results: Invasive anal canal carcinoma histology.
  evidence:
  - reference: PMID:41452529
    reference_title: "Cancer epidemiology in rare and hereditary colorectal diseases 2) anal canal cancer (cancer statistics)."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Clinicopathological features, human papillomavirus (HPV) status, treatment trends, and survival were analyzed."
    explanation: >-
      Registry-based clinicopathological characterization of anal canal
      carcinoma supports histopathologic confirmation and HPV status as
      central to diagnosis and treatment planning.
- name: High-resolution anoscopy with HPV testing
  description: >-
    High-resolution anoscopy with directed biopsy of acetowhite lesions and
    high-risk HPV testing supports detection of high-grade anal
    intraepithelial neoplasia and early invasive disease, particularly in
    high-risk populations (people living with HIV, MSM, immunosuppressed).
  diagnosis_term:
    preferred_term: clinical assessment
    term:
      id: MAXO:0000487
      label: clinical assessment
  markers: high-risk HPV DNA
  results: Detection of high-risk HPV and/or high-grade anal intraepithelial neoplasia.
  evidence:
  - reference: PMID:40019005
    reference_title: "Recent Guidelines on Anal Cancer Screening: A Systematic Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "High-resolution anoscopy was recommended during follow-ups for individuals with abnormal results"
    explanation: >-
      Multiple society guidelines recommend high-resolution anoscopy in
      the diagnostic pathway for anal cancer screening, supporting its
      role in detection of high-grade anal intraepithelial neoplasia and
      early invasive disease in high-risk populations.
treatments:
- name: HPV Vaccination
  description: >-
    Prophylactic vaccination against high-risk HPV types prevents anogenital
    HPV infection and reduces the incidence of anal high-grade squamous
    intraepithelial lesions and anal cancer. Most effective when given before
    HPV exposure.
  treatment_term:
    preferred_term: vaccination
    term:
      id: MAXO:0001017
      label: vaccination
  evidence:
  - reference: PMID:42101137
    reference_title: "Causative Human Papillomavirus (HPV) Genotypes of Anal Cancers in Australian Cisgender Women."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "All cases in this sample could potentially have been prevented by nonavalent prophylactic vaccination, and 97% by the quadrivalent vaccine."
    explanation: >-
      Lesion-specific HPV genotyping of anal squamous cell carcinomas in
      women indicates that nonavalent (and largely quadrivalent) HPV
      vaccination could prevent the great majority of HPV-driven anal
      cancers, supporting HPV vaccination as primary prevention.
- name: Chemoradiation (Nigro regimen)
  description: >-
    Concurrent 5-fluorouracil and mitomycin-C with external-beam radiation
    therapy is the standard curative treatment for localized anal canal
    squamous cell carcinoma, preserving anal sphincter function and avoiding
    upfront abdominoperineal resection.
  treatment_term:
    preferred_term: radiation therapy
    term:
      id: MAXO:0000014
      label: radiation therapy
    therapeutic_agent:
    - preferred_term: 5-fluorouracil
      term:
        id: CHEBI:46345
        label: 5-fluorouracil
    - preferred_term: mitomycin C
      term:
        id: CHEBI:27504
        label: mitomycin C
  evidence:
  - reference: PMID:15571466
    reference_title: "Chemotherapeutic options in the management of anal cancer."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Since the original contribution by Nigro in 1974, surprisingly few changes have been made to the standard of care in chemotherapy, which still consists of a combination of 5-fluorouracil and mitomycin C."
    explanation: >-
      Establishes 5-fluorouracil plus mitomycin C combined with radiation
      (the Nigro regimen) as the long-standing standard chemoradiation
      backbone for anal canal cancer.
  - reference: PMID:41452529
    reference_title: "Cancer epidemiology in rare and hereditary colorectal diseases 2) anal canal cancer (cancer statistics)."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The adoption of chemoradiotherapy (CRT) increased from 14% in the 1990 s to over 80% after 2010, achieving survival outcomes comparable to surgery."
    explanation: >-
      Registry data document the shift from primary surgery to
      chemoradiation as the dominant curative treatment for anal canal
      carcinoma, supporting its role as standard curative therapy.
- name: Salvage Abdominoperineal Resection
  description: >-
    Surgical removal of the anus, rectum, and surrounding tissues with
    permanent colostomy is reserved for residual or recurrent anal canal
    carcinoma after definitive chemoradiation.
  treatment_term:
    preferred_term: surgical procedure
    term:
      id: MAXO:0000004
      label: surgical procedure
  evidence:
  - reference: PMID:37210274
    reference_title: "Survival outcomes following salvage abdominoperineal resection for recurrent and persistent anal squamous cell carcinoma."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The primary treatment for locoregional failure following chemoradiotherapy for squamous cell carcinoma of the anus (SCCA) is salvage abdominoperineal resection (APR)."
    explanation: >-
      Multicenter retrospective cohort supports salvage abdominoperineal
      resection as the standard treatment for locoregional failure after
      definitive chemoradiation for anal squamous cell carcinoma.
- name: Immune Checkpoint Inhibitor Therapy
  description: >-
    PD-1 inhibitors such as pembrolizumab and nivolumab have demonstrated
    activity in recurrent or metastatic anal canal squamous cell carcinoma
    and are used in the second-line and beyond setting.
  treatment_term:
    preferred_term: immunotherapy
    term:
      id: NCIT:C15262
      label: Immunotherapy
    therapeutic_agent:
    - preferred_term: pembrolizumab
      term:
        id: NCIT:C106432
        label: Pembrolizumab
  evidence:
  - reference: PMID:35114169
    reference_title: "Pembrolizumab for previously treated advanced anal squamous cell carcinoma: results from the non-randomised, multicohort, multicentre, phase 2 KEYNOTE-158 study."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Pembrolizumab monotherapy is a possible treatment option with a favourable benefit-risk ratio for patients with previously treated advanced anal squamous cell carcinoma who have no alternative satisfactory treatment options."
    explanation: >-
      Phase 2 KEYNOTE-158 cohort supports pembrolizumab as an active
      second-line treatment for advanced anal squamous cell carcinoma.
  target_mechanisms:
  - target: Adaptive Immune Resistance
    treatment_effect: INHIBITS
    description: >-
      PD-1 blockade with pembrolizumab counteracts adaptive immune
      resistance by interrupting PD-1/PD-L1 signaling between
      tumor-infiltrating T cells and PD-L1-expressing anal squamous
      cell carcinoma cells, restoring anti-tumor T cell activity.
    evidence:
    - reference: PMID:35114169
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Pembrolizumab monotherapy is a possible treatment option with a favourable benefit-risk ratio for patients with previously treated advanced anal squamous cell carcinoma who have no alternative satisfactory treatment options."
      explanation: >-
        Clinical activity of pembrolizumab in advanced anal squamous
        cell carcinoma supports targeting PD-1-mediated adaptive immune
        resistance as a therapeutically relevant mechanism.
disease_term:
  preferred_term: anal canal carcinoma
  term:
    id: MONDO:0007108
    label: anal canal carcinoma

classifications:
  icdo_morphology:
    classification_value: Carcinoma
  harrisons_chapter:
  - classification_value: cancer
  - classification_value: solid tumor

datasets: []

📚

References & Deep Research

Deep Research

1

Anal Canal Carcinoma Deep Research Fallback ▸

Anal Canal Carcinoma Deep Research Fallback

Provider Attempts

2026-05-13T00:00Z: just research-disorder asta Anal_Canal_Carcinoma failed: agentapi not found in PATH and no provider API keys configured (OPENAI_API_KEY, EDISON_API_KEY, ASTA_API_KEY, PERPLEXITY_API_KEY all unset in this environment).
2026-05-13T00:00Z: just research-disorder openai Anal_Canal_Carcinoma failed for the same reason.
2026-05-13T00:00Z: just research-disorder perplexity Anal_Canal_Carcinoma failed for the same reason.
2026-05-13T00:00Z: just research-disorder falcon Anal_Canal_Carcinoma failed for the same reason.

No provider-generated research artifact was available to integrate. Curation therefore proceeded from previously fetched PubMed abstracts in references_cache/, without hand-editing any cache files.

Literature Synthesis

The following PMIDs were used to anchor the curated kb/disorders/Anal_Canal_Carcinoma.yaml entry. Each citation below corresponds to the cached abstract in references_cache/PMID_<id>.md and is attributed to the role it plays in the pathophysiology/clinical model.

HPV etiology and viral mechanism

PMID:42101137 (J Med Virol 2026) — "Causative Human Papillomavirus (HPV) Genotypes of Anal Cancers in Australian Cisgender Women." Laser-capture microdissection of anal SCC lesions attributed HPV-16 as the causal genotype in the great majority of cases (93.3% HPV16). Anchors the HPV-16-dominant etiology, the infectious_agent and environmental entries for HPV, the HPV vaccination prevention rationale, and the higher risk of anal cancer in MSM living with HIV.
PMID:2175676 (Cell 1990) — "The E6 oncoprotein encoded by human papillomavirus types 16 and 18 promotes the degradation of p53." Classic biochemical study showing that the E6 proteins of oncogenic HPV types stimulate ATP- and ubiquitin-proteasome-dependent degradation of p53. Anchors the E6 Oncoprotein-Mediated p53 Degradation pathophysiology node and the upstream half of the HPV → p53 loss → genomic instability axis.
PMID:2537532 (Science 1989) — "The human papilloma virus-16 E7 oncoprotein is able to bind to the retinoblastoma gene product." Founding biochemical evidence that HPV-16 E7 binds and inactivates pRB. Anchors the E7 Oncoprotein-Mediated pRB Inactivation pathophysiology node and the upstream half of the E7 → pRB inactivation → uncontrolled S-phase entry axis.

Risk factors and natural history

PMID:15241823 (Cancer 2004) — "Human papillomavirus, smoking, and sexual practices in the etiology of anal cancer." Population-based case-control study identifying current cigarette smoking as an independent risk factor for anal cancer in both men and women, independent of HPV-related sexual exposures. Anchors the tobacco-smoking entry under environmental.
PMID:40019005 (J Low Genit Tract Dis 2025) — "Recent Guidelines on Anal Cancer Screening: A Systematic Review." Systematic review of society screening guidelines describing the AIN-to-invasive-SCC progression pathway, the role of high-resolution anoscopy in high-risk groups, and the benefit of treating precancerous anal lesions. Anchors the Anal Intraepithelial Neoplasia Progression pathophysiology node and the high-resolution anoscopy diagnostic entry.

Molecular and immune profiling

PMID:34790403 (J Gastrointest Oncol 2021) — "Molecular characterization of squamous cell carcinoma of the anal canal." Multiplatform molecular profiling of 311 anal SCC specimens reporting recurrent somatic mutations in PIK3CA (28.1%), KMT2D (19.5%), FBXW7 (12%), TP53 (12%), and PTEN (10.8%), as well as PD-L1 expression in 40.5% of tumors and PD-1 expression on infiltrating cells in 68.8%. Anchors the Genomic Instability and Adaptive Immune Resistance pathophysiology nodes, the TP53 and PIK3CA genetic entries, the histopathology entry for anal SCC, and the rationale for PD-1 checkpoint blockade.

Clinical presentation and regional spread

PMID:33085290 ("Rectal Bleeding.") — Reference clinical definition of hematochezia as the passage of frank blood per rectum. Anchors the Rectal Bleeding (Hematochezia) phenotype entry as the most common presenting symptom of anal canal cancer.
PMID:37731305 (Ann Palliat Med 2023) — "Palliative care in colorectal and anal malignancies from diagnosis to death." Palliative care review of colorectal and anal malignancies documenting pain among the multiple symptoms commonly experienced by patients with these cancers. Anchors the Anal Pain phenotype entry; the description was deliberately scoped to the palliative-care evidence base (see Round-2 review fix).
PMID:39882228 (J Anus Rectum Colon 2025) — "Metastatic Status and Dissection Effect of Regional/Extraregional Lymph Nodes in Japanese Patients with Squamous Cell Carcinoma of the Anal Canal." Multicenter retrospective cohort of 435 anal canal SCC patients documenting that primary tumor progression is associated with inguinal lymph node metastasis and recurrence. Anchors the Inguinal Lymphadenopathy phenotype entry and the lymphatic drainage pattern of the anal canal below the dentate line.

Epidemiology, histology, and treatment

PMID:41452529 (Int J Clin Oncol 2026) — "Cancer epidemiology in rare and hereditary colorectal diseases 2) anal canal cancer (cancer statistics)." Japanese and Western registry data documenting that anal canal cancer histology varies by population (Japan: 66.8–75.5% adenocarcinoma, 16.2–24.4% SCC; Western: 70–85% SCC), that HPV-16 is the most prevalent genotype in HPV-positive SCC (85% HPV-positive), and that adoption of chemoradiotherapy rose from 14% in the 1990s to >80% after
Anchors the SCC and adenocarcinoma subtype/histopathology entries, the HPV infection pathophysiology node, the histopathology diagnostic entry, and the Nigro-regimen chemoradiation treatment entry.
PMID:15571466 (Expert Opin Pharmacother 2004) — "Chemotherapeutic options in the management of anal cancer." Review establishing that, since Nigro's original 1974 contribution, the chemotherapy backbone for anal cancer has remained 5-fluorouracil plus mitomycin C, given concurrently with radiation. Anchors the Chemoradiation (Nigro regimen) treatment entry and the use of 5-FU and mitomycin C as therapeutic_agent values.
PMID:37210274 (Eur J Surg Oncol 2023) — "Survival outcomes following salvage abdominoperineal resection for recurrent and persistent anal squamous cell carcinoma." Multicenter retrospective cohort establishing salvage abdominoperineal resection as the primary treatment for locoregional failure after chemoradiation for anal SCC. Anchors the Salvage Abdominoperineal Resection treatment entry.
PMID:35114169 (Lancet Gastroenterol Hepatol 2022) — "Pembrolizumab for previously treated advanced anal squamous cell carcinoma: results from the non-randomised, multicohort, multicentre, phase 2 KEYNOTE-158 study." Phase 2 KEYNOTE-158 anal SCC cohort supporting pembrolizumab as an active second-line treatment for advanced anal SCC. Anchors the Immune Checkpoint Inhibitor Therapy treatment entry and the target_mechanisms link from PD-1 blockade to the Adaptive Immune Resistance pathophysiology node (immune_checkpoint_blockade module conformance).

Curation Conclusions

The accepted disease model for HPV-associated anal canal carcinoma is a multi-step transformation in which:

Persistent infection of basal stratified squamous epithelial cells of the anal canal (predominantly at the transformation zone) with high-risk HPV (most commonly HPV-16) establishes sustained expression of the viral oncoproteins E6 and E7.
E6 targets p53 for ubiquitin-proteasome-dependent degradation (PMID:2175676), abolishing DNA damage checkpoints and apoptotic responses.
E7 binds and inactivates pRB (PMID:2537532), releasing E2F transcription factors and driving uncontrolled G1/S transition and proliferation.
Combined p53 and pRB inactivation, together with HPV-associated chromosomal aberrations, produces genomic instability and accumulation of driver mutations (PIK3CA, KMT2D, FBXW7, TP53, PTEN; PMID:34790403).
HPV-driven dysplasia of the anal squamous epithelium progresses through AIN1 → AIN2 → AIN3/HSIL → invasive squamous cell carcinoma (PMID:40019005).
Invasive anal SCC frequently upregulates PD-L1 and engages adaptive immune resistance (PMID:34790403), providing the therapeutic rationale for PD-1 blockade (PMID:35114169).

Clinically, anal canal carcinoma presents most commonly with hematochezia (PMID:33085290), anal pain (PMID:37731305), and inguinal lymphadenopathy in regional spread (PMID:39882228). HIV infection (especially in MSM) and tobacco smoking are major risk modifiers (PMID:42101137, PMID:15241823). Standard curative treatment for localized disease is the Nigro regimen of concurrent 5-FU/mitomycin-C chemoradiation (PMID:15571466, PMID:41452529), with salvage abdominoperineal resection reserved for locoregional failure (PMID:37210274), and PD-1 inhibitors (pembrolizumab, nivolumab) for recurrent or metastatic disease (PMID:35114169).

Subtypes

Curated subtypes in the YAML:

Anal Canal Squamous Cell Carcinoma (NCIT:C7469) — dominant histology in Western series, strongly HPV-16-driven (PMID:42101137).
Anal Canal Adenocarcinoma (NCIT:C7471) — rare in Western series, but more common than SCC in Japanese registries (PMID:41452529); not HPV-associated; treated more like rectal adenocarcinoma.

Items Intentionally Skipped

KMT2D, FBXW7, and PTEN are cited in the Genomic Instability pathophysiology node via PMID:34790403 but are not yet broken out as individual genetic entries. A follow-up curation pass can split these into per-gene entries (with the same snippet as the parent entry) if schema-level gene-level granularity is desired.
The Nigro regimen treatment_term currently uses MAXO:0000014 (radiation therapy) with 5-FU and mitomycin C as therapeutic_agent values. NCIT:C94626 (Chemoradiotherapy) would better represent the combined-modality nature of the regimen; this is a follow-up refinement flagged in Round-3 review.

Anal Canal Carcinoma

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Classifications

Subtypes

Pathophysiology

Histopathology

Pathograph

Phenotypes

Genetic Associations

Treatments

Environmental Factors

Biochemical Markers

Source YAML

References & Deep Research

Deep Research

Anal Canal Carcinoma Deep Research Fallback

Provider Attempts

Literature Synthesis

HPV etiology and viral mechanism

Risk factors and natural history

Molecular and immune profiling

Clinical presentation and regional spread

Epidemiology, histology, and treatment

Curation Conclusions

Subtypes

Items Intentionally Skipped