Ovarian Endometrioid Carcinoma

Disease Information

Disease Name: Ovarian Endometrioid Carcinoma (OEC)

Category: Epithelial ovarian cancer, gynecologic malignancy

Definition and Classification

Ovarian endometrioid carcinoma is a distinct histologic subtype of epithelial ovarian cancer that accounts for approximately 10% of all ovarian carcinomas (yoshida2025molecularpathologyof pages 1-3). According to the 2020 World Health Organization (WHO) classification, OEC is defined as a carcinoma resembling endometrioid carcinoma of the uterine corpus, characterized by tubular glands resembling proliferative endometrial epithelium (yoshida2025molecularpathologyof pages 1-3, leo2021whatisnew pages 1-2). The WHO Classification of Female Genital Tumours (5th edition, 2020) recognizes OEC as one of five principal histotypes of ovarian carcinoma, alongside high-grade serous, low-grade serous, clear cell, and mucinous carcinomas (leo2021whatisnew pages 1-2, kobel2022theevolutionof pages 1-3).

OEC exhibits broad morphological diversity, often including glandular, solid, squamous, or sertoliform patterns, which can lead to diagnostic confusion with other primary ovarian neoplasms or metastatic tumors (yoshida2025molecularpathologyof pages 1-3). While earlier studies reported higher frequencies of OEC, this discrepancy likely reflects historical misclassification, particularly of SET (Solid, pseudo-Endometrioid, and Transitional cell-like)-pattern high-grade serous carcinomas as high-grade OECs (yoshida2025molecularpathologyof pages 1-3).

Common Synonyms

• Endometrioid ovarian carcinoma
• Ovarian endometrioid adenocarcinoma
• Endometriosis-associated ovarian cancer (when arising from endometriosis, shared with clear cell carcinoma)

Key Identifiers

While specific OMIM, Orphanet, or MONDO identifiers were not detailed in the reviewed literature, OEC is classified under ICD-O morphology codes for endometrioid carcinoma and is part of the broader category of epithelial ovarian neoplasms.

Epidemiology and Population Demographics

Global Incidence and Prevalence

Globally, an estimated 29,319 new patients of endometrioid cancer were identified in 2020 among all ovarian cancer cases (wang2024globalincidenceof pages 1-2). This represents approximately 9.5-10% of all epithelial ovarian carcinomas worldwide (yoshida2025molecularpathologyof pages 1-3, wang2024globalincidenceof pages 1-2).

The distribution of ovarian cancer histologic subtypes exhibits regional variation. Northern Africa and Eastern Asia show the highest burden of endometrioid carcinomas, contrasting with high-grade serous carcinomas which predominate in Eastern Europe (wang2024globalincidenceof pages 1-2). Recent studies employing refined pathological classification consistently report the frequency of OEC as around 10%, with no significant difference between Western and Asian populations, unlike ovarian clear cell carcinoma which is more prevalent among Asian women (yoshida2025molecularpathologyof pages 1-3).

In the United States, during 1992-2019, endometrioid ovarian cancer incidence showed differential trends by race/ethnicity. Endometrioid cancer incidence decreased in non-Hispanic White women (AAPC during 2010-2019 = -1.3; 95% CI, -1.9 to -0.8) but increased in Hispanic women (AAPC = 3.6; 95% CI, 1.0 to 6.3) (phung2023trendsofovarian pages 1-2).

Age Distribution

In Japan, OEC is increasingly diagnosed in younger women (<50 years) and in early-stage disease (yoshida2025molecularpathologyof pages 1-3). This trend may reflect rising prevalence of endometriosis, increased lifetime menstrual cycles due to declining fertility, delayed marriage, earlier menarche, and later menopause, as well as growing prevalence of obesity (yoshida2025molecularpathologyof pages 1-3). These factors are thought to be influenced by recent societal and lifestyle changes that impact reproductive and hormonal health.

Sex Ratio

Ovarian endometrioid carcinoma, like all ovarian cancers, affects exclusively or overwhelmingly female patients, as it arises from ovarian or endometriotic tissue.

Etiology

Disease Causal Factors

Endometriosis as Precursor

Endometriosis is a well-established risk factor and potential precursor for OEC, conferring a two- to threefold increase in risk, a feature shared with ovarian clear cell carcinoma (yoshida2025molecularpathologyof pages 1-3). Histological evidence of endometriosis is observed in approximately 40% of resected OEC specimens (yoshida2025molecularpathologyof pages 1-3). The presence of shared somatic mutations between endometriotic lesions and OEC—such as ARID1A loss-of-function and PIK3CA gain-of-function mutations—supports the hypothesis that OEC may arise from endometriosis through stepwise malignant transformation (yoshida2025molecularpathologyof pages 1-3).

Endometriosis affects 10-18% of reproductive-aged women and is associated with a 2-3% lifetime risk of ovarian cancer, exceeding that of the general female population (yoshida2025molecularpathologyof pages 1-3). Notably, even morphologically benign endometriotic lesions harbor oncogenic mutations (e.g., ARID1A, PIK3CA, KRAS, PTEN, TP53), indicating their potential as precursors to malignancy (yoshida2025molecularpathologyof pages 1-3).

Risk Factors

Genetic Risk Factors: - Lynch Syndrome: OEC is enriched for Lynch syndrome-associated tumors. Among mismatch repair-deficient (MMRd) ovarian endometrioid carcinomas, approximately 9.5% are associated with Lynch syndrome, supporting routine MMR testing (yoshida2025molecularpathologyof pages 1-3, kobel2022theevolutionof pages 1-3). - BRCA1/2 Mutations: BRCA1 mutation carriers show increased risks for endometrioid EC (SIR = 2.63, 95% CI: 1.80-3.83; HR = 2.01, 95% CI: 1.18-3.45), although the association is stronger for serous-like tumors (ali2023epidemiologyandrisk pages 1-2).

Environmental/Lifestyle Risk Factors: - Obesity: 1.2-fold increase in risk per 5 kg/m² increase in body mass index (BMI) (yoshida2025molecularpathologyof pages 1-3) - Hormone Replacement Therapy (HRT): Relative risk ~1.3-1.4 (yoshida2025molecularpathologyof pages 1-3, ali2023epidemiologyandrisk pages 1-2) - Elevated Estrogen Exposure: Greater number of lifetime menstrual cycles associated with increased risk (yoshida2025molecularpathologyof pages 1-3) - Nulliparity: Nulliparous women have higher risk (ali2023epidemiologyandrisk pages 1-2)

OEC shows stronger associations with family history of ovarian cancer and higher BMI, features not typically observed in clear cell carcinoma despite both subtypes' association with endometriosis (yoshida2025molecularpathologyof pages 1-3).

Protective Factors

Reproductive Factors: - Parity: Each birth reduces risk by approximately 10% (yoshida2025molecularpathologyof pages 1-3) - Oral Contraceptive Use: 15-20% risk reduction with five years of use (yoshida2025molecularpathologyof pages 1-3)

Surgical Interventions: - Tubal Ligation and Salpingectomy: Appear protective, possibly by reducing retrograde menstruation (yoshida2025molecularpathologyof pages 1-3)

Tobacco: - Smoking: Interestingly, unlike other ovarian cancer subtypes, smoking was correlated with a lower risk for OEC (relative risk ~0.8) (yoshida2025molecularpathologyof pages 1-3)

Genetic and Molecular Information

Causal Genes and Pathogenic Variants

Table: This table summarizes the major recurrent molecular alterations and pathway-level abnormalities reported in ovarian endometrioid carcinoma, including their biologic effects and clinical implications. It is useful for linking histology, molecular subtype, prognosis, and potential therapeutic opportunities.

The molecular landscape of OEC is characterized by recurrent alterations in chromatin remodeling genes, the PI3K/AKT/mTOR signaling pathway, and DNA mismatch repair genes. Key findings include:

ARID1A (AT-rich Interaction Domain 1A): - Frequent loss-of-function alterations, often reflected by loss of protein expression on immunohistochemistry - Disrupts SWI/SNF chromatin remodeling complex - Often co-occurs with PIK3CA mutations - Shared between endometriotic lesions and OEC, supporting progression model (yoshida2025molecularpathologyof pages 1-3, leo2021whatisnew pages 1-2)

PIK3CA (Phosphatidylinositol-4,5-Bisphosphate 3-Kinase Catalytic Subunit Alpha): - Activating/gain-of-function mutations - Frequently co-occurs with ARID1A loss - Present in endometriosis-related precursor lesions - Activates PI3K/AKT/mTOR signaling pathway (yoshida2025molecularpathologyof pages 1-3, leo2021whatisnew pages 1-2)

PTEN (Phosphatase and Tensin Homolog): - Inactivating mutations/loss of function - Characteristic of endometrioid tumors - Releases inhibition of PI3K signaling - Frequently present in OEC (leo2021whatisnew pages 1-2, yoshida2025molecularpathologyof pages 1-3)

CTNNB1 (Catenin Beta 1): - Activating mutations leading to β-catenin pathway alterations - Characteristic/recurrent in OEC - Helpful lineage-defining alteration for endometrioid histotype (leo2021whatisnew pages 1-2, yoshida2025molecularpathologyof pages 1-3)

KRAS: - Activating mutations, less common than PTEN/PIK3CA/CTNNB1 - Also seen in benign endometriotic lesions (yoshida2025molecularpathologyof pages 1-3)

MMR Genes (MLH1, MSH2, MSH6, PMS2): - Loss of expression from germline or somatic mutations, or MLH1 promoter hypermethylation - Define the MMRd molecular subtype (25-30% of OEC) - Enriched for Lynch syndrome-associated tumors - Confer microsatellite instability (MSI) and hypermutation (yoshida2025molecularpathologyof pages 1-3, kobel2022theevolutionof pages 1-3)

POLE (DNA Polymerase Epsilon, Catalytic Subunit): - Pathogenic exonuclease-domain mutations causing ultramutation - Uncommon but clinically important subset - Associated with excellent prognosis (yoshida2025molecularpathologyof pages 1-3, kobel2022theevolutionof pages 1-3)

Molecular Subtypes

Recent data demonstrate that the endometrial cancer molecular taxonomy applies to OEC, enabling classification into four molecular subtypes (yoshida2025molecularpathologyof pages 1-3, kobel2022theevolutionof pages 1-3):

1. POLE-ultramutated: Excellent prognosis, candidates for treatment de-escalation
2. Mismatch Repair-Deficient (MMRd): Generally excellent outcomes, immunotherapy-sensitive, enriched for Lynch syndrome
3. p53-abnormal: Poorer prognosis, warrant intensified management
4. No Specific Molecular Profile (NSMP): Heterogeneous, often enriched for PI3K/Wnt pathway alterations

Allele Frequencies

Specific population allele frequencies were not detailed in the reviewed literature, though mutations are predominantly somatic rather than germline (except in Lynch syndrome and hereditary cancer predisposition syndromes).

Mechanism / Pathophysiology

Molecular Pathways

PI3K/AKT/mTOR Pathway: The PI3K/AKT/mTOR pathway is aberrantly activated in OEC, driven by PIK3CA gain-of-function mutations and/or PTEN loss. This pathway activation promotes cell proliferation, survival, metabolic rewiring, and progression from endometriosis to invasive carcinoma (yoshida2025molecularpathologyof pages 1-3). The pathway represents a major translational target, with PI3K/AKT/mTOR inhibitors under investigation (yoshida2025molecularpathologyof pages 1-3).

Wnt/β-Catenin Pathway: CTNNB1 alterations activate Wnt/β-catenin signaling, affecting epithelial differentiation, proliferation, and glandular/squamous morphology. This pathway reinforces the endometrioid lineage program and is characteristic of endometrioid differentiation (leo2021whatisnew pages 1-2, yoshida2025molecularpathologyof pages 1-3).

DNA Mismatch Repair Pathway: MMR deficiency in approximately 25-30% of OEC leads to microsatellite instability (MSI) and hypermutation, creating high tumor mutational burden and neoantigen load. This confers sensitivity to immune checkpoint inhibitors (yoshida2025molecularpathologyof pages 1-3, kobel2022theevolutionof pages 1-3).

Chromatin Remodeling: ARID1A loss disrupts the SWI/SNF chromatin remodeling complex, altering transcriptional control and differentiation programs. This creates vulnerability to synthetic lethal approaches including ATR inhibitors and epigenetic modulators (yoshida2025molecularpathologyof pages 1-3).

Cellular Processes

Stepwise Malignant Transformation: The progression from benign endometriosis to atypical endometriosis to invasive OEC is supported by the presence of shared mutations (ARID1A, PIK3CA) in morphologically benign endometriotic lesions, indicating their potential as precursors (yoshida2025molecularpathologyof pages 1-3). This model suggests that oncogenic alterations accumulate progressively, with inflammatory signaling and oxidative stress in the endometriotic microenvironment contributing to transformation.

Epigenetic Changes: In sporadic MMRd cases, MLH1 promoter hypermethylation is the predominant mechanism of MMR deficiency, contrasting with germline mutations in Lynch syndrome-associated cases (yoshida2025molecularpathologyof pages 1-3).

Tumor Microenvironment

The tumor immune microenvironment differs between OEC and high-grade serous ovarian cancer, with endometrioid ovarian cancer potentially more conducive to immunotherapy due to lower levels of immune exclusion and T cell exhaustion (kobel2022theevolutionof pages 1-3).

Suggested Ontology Terms

Gene Ontology (GO) Terms: - GO:0006281 (DNA repair) - GO:0006974 (cellular response to DNA damage stimulus) - GO:0006281 (DNA mismatch repair) - GO:0016568 (chromatin modification) - GO:0006338 (chromatin remodeling) - GO:0007049 (cell cycle) - GO:0016310 (phosphorylation) - GO:0043066 (negative regulation of apoptotic process) - GO:0071310 (cellular response to organic substance)

Cell Type (CL) Terms: - CL:0002319 (neural cell) - CL:0000066 (epithelial cell) - CL:0000583 (glandular epithelial cell) - CL:0002293 (epithelial cell of endometrium)

Anatomical Structures Affected

Organ and Tissue Level

Primary Site: - Ovary (UBERON:0000992): Primary organ of tumor development - Endometriotic tissue: When arising from endometriosis, can involve peritoneum, fallopian tubes, bowel surfaces, and other pelvic structures

Associated with Endometriosis: Approximately 40% of OEC cases show histological evidence of associated endometriosis. Endometriosis can involve ovarian endometriomas (cysts), peritoneal implants, and deep infiltrating lesions (yoshida2025molecularpathologyof pages 1-3).

Secondary Involvement: - Pelvic peritoneum - Omentum - Pelvic and para-aortic lymph nodes (in advanced/metastatic disease) - Less commonly: liver, lungs, and other distant sites

Cellular Level

OEC arises from epithelial cells, specifically glandular epithelial cells that resemble endometrial-type epithelium. The tumor is characterized by tubular glands resembling proliferative endometrial epithelium, with variable solid, squamous, or sertoliform differentiation patterns (yoshida2025molecularpathologyof pages 1-3, leo2021whatisnew pages 1-2).

Suggested CL Terms: - CL:0000066 (epithelial cell) - CL:0000583 (glandular epithelial cell) - CL:0002293 (epithelial cell of endometrium)

Subcellular Level

GO Cellular Component Terms: - GO:0005634 (nucleus) - site of chromatin remodeling defects and p53 alterations - GO:0005886 (plasma membrane) - location of receptor signaling - GO:0005737 (cytoplasm) - site of PI3K/AKT/mTOR signaling - GO:0000228 (nuclear chromosome) - affected by chromatin remodeling defects

Temporal Development

Onset

Age of Onset: OEC typically presents in adult women, with increasing diagnosis in younger women (<50 years) in some populations like Japan (yoshida2025molecularpathologyof pages 1-3). The median age at diagnosis for ovarian cancer overall is around 63 years, though OEC may present somewhat earlier given its association with endometriosis, which affects reproductive-age women (ali2023epidemiologyandrisk pages 1-2).

Onset Pattern: Generally insidious, as ovarian cancer often presents with non-specific symptoms and is frequently diagnosed at advanced stages (III or IV) (ali2023epidemiologyandrisk pages 1-2). However, OEC is more often diagnosed at earlier stages compared to high-grade serous carcinoma (hayashi2023molecularhistopathologyfor pages 1-2, yoshida2025molecularpathologyof pages 1-3).

Progression

Disease Course: OEC typically follows a progressive course from precursor endometriotic lesions (in endometriosis-associated cases) through atypical endometriosis to invasive carcinoma. OEC is typically of low grade with a generally favorable prognosis compared to high-grade serous carcinoma, though high-grade/p53-abnormal OEC behaves more aggressively (hayashi2023molecularhistopathologyfor pages 1-2, yoshida2025molecularpathologyof pages 1-3).

Disease Staging: The FIGO 2023 staging system for endometrial cancer integrates molecular classification, and similar principles are being applied to ovarian endometrioid carcinoma. Staging includes assessment of: - Stage I: Tumor confined to ovaries - Stage II: Tumor involves one or both ovaries with pelvic extension - Stage III: Tumor involves one or both ovaries with peritoneal implants outside pelvis and/or lymph node metastases - Stage IV: Distant metastases (kobel2022theevolutionof pages 1-3)

Molecular Subtype and Prognosis: - POLE-mutated and MMRd subsets: Generally excellent outcomes - p53-abnormal/high-grade tumors: Poorer prognosis requiring intensified management - NSMP: Intermediate prognosis (yoshida2025molecularpathologyof pages 1-3, kobel2022theevolutionof pages 1-3)

Diagnostics

Clinical Tests and Biomarkers

Serum Biomarkers: - CA125: Elevated in many ovarian cancers but with low specificity - HE4 (Human Epididymis Protein 4): Combined with CA125 improves detection sensitivity and specificity for ovarian cancer (kobel2022theevolutionof pages 1-3)

Imaging Studies

MRI (Magnetic Resonance Imaging): MRI is valuable for characterizing ovarian masses. MRI-based radiomics analysis can differentiate ovarian clear cell carcinoma from endometrioid carcinoma with high accuracy (kobel2022theevolutionof pages 1-3).

Histopathology

Microscopic Features: - Tubular glands resembling proliferative endometrial epithelium - Variable patterns: glandular, solid, squamous, sertoliform - May show squamous metaplasia (yoshida2025molecularpathologyof pages 1-3, leo2021whatisnew pages 1-2)

Immunohistochemical Markers: A four-marker IHC panel (WT1/p53/napsin A/PR) can distinguish the five principal ovarian carcinoma histotypes with high accuracy: - WT1: Typically negative in OEC (positive in serous) - p53: Variable; abnormal pattern in p53-abnormal molecular subtype - Napsin A: Negative in OEC (positive in clear cell) - PR (Progesterone Receptor): Often positive in OEC (kobel2022theevolutionof pages 1-3)

Genetic and Molecular Testing

MMR Immunohistochemistry (Routine Recommended): Assessment of MLH1, MSH2, MSH6, and PMS2 protein expression is recommended for all OEC cases to: - Identify MMRd molecular subtype - Screen for Lynch syndrome - Predict immunotherapy sensitivity (yoshida2025molecularpathologyof pages 1-3, kobel2022theevolutionof pages 1-3)

MSI Testing: PCR-based microsatellite instability analysis using NCI-recommended loci can confirm MMRd status (kobel2022theevolutionof pages 1-3).

MLH1 Promoter Methylation Testing: For cases with MLH1/PMS2 loss, methylation testing helps distinguish sporadic (hypermethylated) from Lynch-associated (unmethylated) cases (yoshida2025molecularpathologyof pages 1-3, kobel2022theevolutionof pages 1-3).

Molecular Subtyping (POLE, MMR, p53, NSMP): Using IHC surrogates and/or sequencing to classify into four molecular subtypes for prognostic stratification and therapeutic selection (yoshida2025molecularpathologyof pages 1-3, kobel2022theevolutionof pages 1-3).

Germline Testing: Indicated for MMRd cases (especially if MLH1 unmethylated) and cases with family history suggestive of hereditary cancer syndromes (yoshida2025molecularpathologyof pages 1-3, kobel2022theevolutionof pages 1-3).

Differential Diagnosis

OEC must be distinguished from: - High-grade serous carcinoma (especially SET pattern) - Clear cell carcinoma - Mucinous carcinoma - Metastatic endometrial carcinoma - Metastatic gastrointestinal carcinoma

Immunohistochemical panels, molecular testing, and clinical correlation are essential for accurate diagnosis (leo2021whatisnew pages 1-2, kobel2022theevolutionof pages 1-3).

Outcome / Prognosis

Survival and Prognosis

OEC generally has a more favorable prognosis compared to high-grade serous carcinoma, particularly when diagnosed at early stages (hayashi2023molecularhistopathologyfor pages 1-2, yoshida2025molecularpathologyof pages 1-3). Prognosis varies significantly by molecular subtype:

By Molecular Subtype: - POLE-mutated: Excellent prognosis, may justify treatment de-escalation - MMRd: Generally excellent outcomes - NSMP: Intermediate prognosis - p53-abnormal/high-grade: Poorer prognosis, requires intensified management (yoshida2025molecularpathologyof pages 1-3, kobel2022theevolutionof pages 1-3)

Lynch Syndrome-Associated OEC: Among mismatch repair-deficient endometrial cancers (which share biological features with MMRd OEC), patients with Lynch syndrome showed a trend towards better recurrence-free survival compared with MLH1-hypermethylated MMRd cases. Five-year recurrence-free survival was 91.7% (95% CI = 83.1%-100%) for Lynch syndrome cases versus 78.6% (95% CI = 73.8%-83.7%) for MLH1-hypermethylated MMRd cases (kobel2022theevolutionof pages 1-3).

Subsequent Cancer Risk: Patients with Lynch syndrome-associated OEC have increased risk of subsequent cancers. The probability of subsequent Lynch-associated cancer at 10 years was 11.6% (95% CI = 0.0%-24.7%) in the Lynch syndrome group (kobel2022theevolutionof pages 1-3).

Prognostic Factors

• Stage at diagnosis: Earlier stage associated with better outcomes
• Tumor grade: Low-grade tumors have better prognosis
• Molecular subtype: POLE-mutated and MMRd subtypes favorable; p53-abnormal unfavorable
• Age: Younger age at diagnosis may be associated with better outcomes
• Residual disease after surgery: Complete cytoreduction associated with improved survival

Treatment

Table: This table summarizes current and emerging treatment strategies for ovarian endometrioid carcinoma, linking each modality to its main indications, available efficacy evidence, and relevant molecular subgroups. It is useful for mapping standard care alongside biomarker-driven precision approaches.

Surgery

Primary Cytoreductive Surgery: Standard initial management includes total hysterectomy with bilateral salpingo-oophorectomy, omentectomy, peritoneal staging/biopsies, and lymph node assessment in selected cases. OEC is often diagnosed at earlier stage than high-grade serous carcinoma, supporting surgery-centered management in localized disease (hayashi2023molecularhistopathologyfor pages 1-2, kobel2022theevolutionof pages 1-3, yoshida2025molecularpathologyof pages 1-3).

Chemotherapy

Standard Regimen: Carboplatin plus paclitaxel is the standard adjuvant chemotherapy for advanced-stage disease and high-risk early-stage cases (hayashi2023molecularhistopathologyfor pages 1-2, kobel2022theevolutionof pages 1-3, yoshida2025molecularpathologyof pages 1-3).

Immunotherapy

Checkpoint Inhibitors: Immune checkpoint inhibitors (pembrolizumab, dostarlimab) have demonstrated remarkable efficacy in MMRd/dMMR tumors:

• In the NRG-GY018 trial in endometrial cancer, 12-month progression-free survival in dMMR disease was 74% with pembrolizumab-chemotherapy versus 38% with placebo-chemotherapy (hazard ratio 0.30; 95% CI, 0.19-0.48; P<0.001) (kobel2022theevolutionof pages 1-3)
• In pMMR disease, median PFS was 13.1 months with pembrolizumab versus 8.7 months with placebo (hazard ratio 0.54; 95% CI, 0.41-0.71; P<0.001) (kobel2022theevolutionof pages 1-3)

The combination of immune checkpoint inhibitors with chemotherapy is now standard for advanced or recurrent MMRd disease. OEC's enrichment for Lynch syndrome-associated/MMRd tumors makes this particularly relevant (yoshida2025molecularpathologyof pages 1-3, kobel2022theevolutionof pages 1-3).

Relevant MAXO Terms: - MAXO:0001175 (chemotherapy) - MAXO:0001479 (immunotherapy) - MAXO:0000571 (surgical procedure)

Targeted Therapy

PI3K/AKT/mTOR Inhibitors: Under investigation for tumors with PIK3CA mutations and/or PTEN loss, which are common in OEC. The PI3K/AKT/mTOR pathway is a major driver and translational target (yoshida2025molecularpathologyof pages 1-3).

ARID1A-Directed Synthetic Lethality: ATR inhibitors and epigenetic modulators are being investigated for ARID1A-deficient tumors, which are frequent in OEC (yoshida2025molecularpathologyof pages 1-3).

PARP Inhibitors: Potential utility in tumors with homologous recombination deficiency or BRCA1/2 mutations. In preclinical models, a BRCA1-mutant endometrioid organoid showed increased olaparib sensitivity (kobel2022theevolutionof pages 1-3).

Hormonal Therapy

Progestin-based therapy may be considered for selected low-grade, hormone receptor-positive, indolent, recurrent, or fertility-sparing cases, by analogy to endometrioid gynecologic tumors (kobel2022theevolutionof pages 1-3, yoshida2025molecularpathologyof pages 1-3).

Molecularly Stratified Treatment

Molecular classification enables risk-stratified management: - POLE-mutated: Excellent prognosis, potential treatment de-escalation - MMRd: Immunotherapy-sensitive - p53-abnormal: Highest-risk biology, intensified management - NSMP: Heterogeneous, often enriched for PI3K/Wnt alterations, potential targets for pathway inhibitors (yoshida2025molecularpathologyof pages 1-3, kobel2022theevolutionof pages 1-3)

Prevention

Primary Prevention

Risk Factor Modification: - Oral Contraceptive Use: 15-20% risk reduction with 5 years of use (yoshida2025molecularpathologyof pages 1-3) - Achieving/Maintaining Healthy Weight: Obesity increases risk; weight management may reduce risk (yoshida2025molecularpathologyof pages 1-3) - Breastfeeding and Parity: Each birth reduces risk by ~10% (yoshida2025molecularpathologyof pages 1-3)

Secondary Prevention

Surgical Risk Reduction: - Tubal Ligation/Salpingectomy: Protective, possibly by reducing retrograde menstruation (yoshida2025molecularpathologyof pages 1-3) - Risk-Reducing Salpingo-Oophorectomy: Considered in high-risk populations (BRCA1/2 carriers, Lynch syndrome) (ali2023epidemiologyandrisk pages 1-2)

Genetic Screening and Counseling

Lynch Syndrome Screening: Universal MMR immunohistochemistry testing of all OEC cases is recommended to identify Lynch syndrome carriers, enabling: - Genetic counseling and germline testing - Surveillance for other Lynch-associated cancers - Cascade testing of at-risk family members (yoshida2025molecularpathologyof pages 1-3, kobel2022theevolutionof pages 1-3)

BRCA1/2 Testing: Consideration of genetic testing in cases with family history of breast/ovarian cancer or personal history suggestive of hereditary cancer syndrome (ali2023epidemiologyandrisk pages 1-2).

Model Organisms and Experimental Models

Patient-Derived Organoids (PDOs)

Patient-derived organoids have been successfully established from OEC tissues, preserving histopathology, molecular subtype characteristics, and genetic profiles including POLE, MMR, p53 status, and pathway alterations (kobel2022theevolutionof pages 1-3). OEC organoids enable: - Drug sensitivity testing (carboplatin, paclitaxel, olaparib) - Correlation with clinical responses - Precision medicine applications (kobel2022theevolutionof pages 1-3)

Patient-Derived Xenografts (PDX)

PDX models in immunodeficient mice (NOD-SCID, NSG) using: - Subcutaneous implantation: Easier monitoring, higher engraftment rates - Orthotopic implantation: Better recapitulates tumor microenvironment and metastatic patterns (kobel2022theevolutionof pages 1-3)

Orthotopic organoid-based PDX (O-PDX) models maintain tissue architecture, biomarker expression, and genetic profiles of original tumors, proving useful for preclinical therapeutic evaluation (kobel2022theevolutionof pages 1-3).

Genetically Engineered Mouse Models (GEMMs)

Models with relevant mutations (Tp53, Pten, Arid1a combinations) have been developed. Syngeneic models from murine fallopian tube organoids with defined genetic alterations enable immunotherapy studies in immunocompetent hosts (kobel2022theevolutionof pages 1-3).

Cell Lines

Limited endometrioid-specific ovarian cancer cell lines are available, making patient-derived models particularly valuable for OEC research (kobel2022theevolutionof pages 1-3).

Applications: - Drug screening and therapeutic response prediction - Mechanistic studies of pathway dependencies - Biomarker validation - Precision medicine approaches

Summary and Clinical Implications

Ovarian endometrioid carcinoma represents approximately 10% of epithelial ovarian cancers and is distinguished by:

1. Strong association with endometriosis (40% of cases), suggesting a progression model from benign to malignant disease
2. Characteristic molecular alterations including ARID1A loss, PIK3CA/PTEN mutations, CTNNB1 alterations, and enrichment for MMR deficiency
3. Four molecular subtypes (POLE-ultramutated, MMRd, p53-abnormal, NSMP) with distinct prognoses and therapeutic implications
4. Enrichment for Lynch syndrome, necessitating universal MMR testing
5. Generally favorable prognosis compared to high-grade serous carcinoma, especially in POLE-mutated and MMRd subtypes
6. Emerging immunotherapy opportunities, particularly for MMRd tumors showing dramatic responses to checkpoint inhibitors
7. Multiple targetable pathways including PI3K/AKT/mTOR, chromatin remodeling, and DNA repair mechanisms

Integrating morphology with molecular classification refines diagnosis and prognostication. Routine MMR immunohistochemistry with reflex germline testing improves Lynch syndrome detection. Future priorities include prospective validation of molecular stratification, multi-omics refinement of NSMP tumors, and development of targeted therapeutic strategies for pathway-driven disease.

Suggested MONDO ID: MONDO:0003573 (ovarian endometrioid adenocarcinoma)

This comprehensive report synthesizes current evidence on ovarian endometrioid carcinoma, providing a foundation for clinical care, research prioritization, and therapeutic development.

References

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7. (hayashi2023molecularhistopathologyfor pages 1-2): Takuma Hayashi and Ikuo Konishi. Molecular histopathology for establishing diagnostic method and clinical therapy for ovarian carcinoma. Journal of Clinical Medicine Research, 15:68-75, Feb 2023. URL: https://doi.org/10.14740/jocmr4853, doi:10.14740/jocmr4853. This article has 25 citations.

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