| Gene | Approx. alteration frequency in UC | Predominant alteration type(s) | Functional consequence | Key pathway / process | NMIBC vs MIBC correlation | Prognostic / biologic association | Therapeutic implications | Evidence |
|---|---:|---|---|---|---|---|---|---|
| **FGFR3** | ~70% of NMIBC; ~15% of MIBC; ~39% of non-muscle-invasive specimens and ~14% of muscle-invasive specimens in one real-world series | Activating hotspot mutations, fusions, overexpression | Gain-of-function; ligand-independent receptor activation, increased proliferation/survival | FGFR/RTK-RAS-MAPK; PI3K-AKT | Strongly enriched in NMIBC and luminal-papillary/luminal-like disease; less common in aggressive MIBC | Often linked to papillary, luminal differentiation and relatively better prognosis than TP53-driven disease, but resistance and heterogeneity occur in advanced disease | FDA-approved FGFR inhibitor **erdafitinib** for susceptible FGFR2/3-altered metastatic UC; resistance via second-site FGFR3 mutations and PI3K-mTOR pathway changes | (pqac-00000001, pqac-00000009, pqac-00000010, pqac-00000011) |
| **TP53** | ~50% of MIBC; nearly half of MIBC in molecular pathology review | Missense/truncating mutations, pathway inactivation; often mutually exclusive with MDM2 amplification and relatively exclusive vs FGFR3 programs | Loss of tumor suppressor function; impaired DNA-damage response, apoptosis, cell-cycle arrest | p53 pathway / cell-cycle checkpoint | Enriched in MIBC, basal/squamous and neuroendocrine-like aggressive disease; less typical of low-grade papillary NMIBC | Associated with genomic instability, invasion, poorer survival, and aggressive phenotypes | Not directly targetable in routine care; may inform risk stratification and subtype biology; abnormal p53 expression may predict response patterns to enfortumab vedotin in exploratory studies | (pqac-00000001, pqac-00000009, pqac-00000010) |
| **TERT promoter / TERT** | Common / among most frequent early alterations in UC; exact % not provided in available contexts | Promoter mutations, increased expression | Telomerase activation and replicative immortality | Telomere maintenance | Occurs across stages, including early urothelial tumorigenesis | Associated with tumor development; higher expression has been linked to poor prognosis in review literature | Potential urine-based molecular biomarker and disease-monitoring target; no standard direct targeted therapy | (pqac-00000001, pqac-00000009) |
| **PIK3CA** | Common recurrent alteration; listed among commonly mutated genes in UC; 45% in one 2025 cohort (external to 2023-24 evidence but consistent with review framing) | Activating hotspot mutations | PI3K pathway activation, enhanced proliferation/survival | PI3K-AKT-mTOR | Seen across UC; co-occurs with FGFR3-rich luminal/NMIBC programs in some genomic landscapes | Supports tumor growth and may contribute to targeted-therapy resistance | Suggests rationale for PI3K/AKT/mTOR-targeted combinations; implicated in resistance to FGFR inhibition | (pqac-00000001, pqac-00000010, pqac-00000011) |
| **RB1** | Recurrent in MIBC; frequency not quantified in available contexts | Inactivating mutation/deletion | Loss of G1/S checkpoint control | RB / cell-cycle control | More characteristic of aggressive, muscle-invasive and neuroendocrine-like disease | Associated with high-grade biology and progression | Primarily prognostic/biologic marker; may support intensified systemic treatment strategies and subtype classification | (pqac-00000001, pqac-00000009, pqac-00000010) |
| **STAG2** | Frequently mutated in NMIBC; exact % not provided in available 2023-24 contexts | Inactivating mutations | Cohesin dysfunction, altered chromatid segregation and genomic regulation | Cohesin / chromosome segregation | Especially noted in NMIBC | Marker of early urothelial tumorigenesis and molecular heterogeneity | Potential biomarker for classification and surveillance; no established direct therapy | (pqac-00000001, pqac-00000011) |
| **CDKN2A** | Recurrent deletion/alteration in UC | Deletion, loss-of-function | Loss of p16-mediated cell-cycle inhibition | CDK4/6-RB axis | Seen in both NMIBC and MIBC; part of chromosome 9 loss events in urothelial tumorigenesis | Contributes to unchecked proliferation and progression | Theoretic rationale for CDK4/6-directed strategies; not yet routine biomarker-guided standard in UC | (pqac-00000010, pqac-00000011) |
| **ERCC2** | Recurrent subset in MIBC; ~20% of SNVs tied to ERCC2-associated mutational signature in one review summary | Missense mutations affecting NER helicase function | Defective nucleotide excision repair, increased mutagenesis | DNA damage response / repair (DDR) | More emphasized in MIBC and treatment-response studies | Associated with tobacco-linked mutational processes and better response to cisplatin-based chemotherapy in DDR-altered tumors | Predictive biomarker candidate for cisplatin sensitivity; also linked to response to radiation and immune checkpoint blockade in DDR-altered UC | (pqac-00000010) |
| **MDM2** | ~7% amplification in MIBC | Amplification | p53 pathway suppression | p53 negative regulation | More relevant in MIBC; generally mutually exclusive with TP53 mutation | Supports aggressive biology through p53 functional silencing | Investigational biomarker; theoretical MDM2-targeting relevance but not standard in UC | (pqac-00000010) |
| **KDM6A / chromatin-modifier genes** | Commonly altered class in UC; exact % not provided in available contexts | Loss-of-function mutations | Epigenetic dysregulation, altered differentiation programs | Chromatin modification / transcriptional control | Present across UC; part of urothelial molecular heterogeneity | May shape subtype identity and progression risk | Supports epigenetic-therapy research and molecular classification, but no routine targeted use | (pqac-00000001, pqac-00000010) |
| **KMT2D / KMT2C / KMT2A** | Recurrently altered; distinct prevalence reported between UTUC and bladder UC | Mutations, likely loss/dysregulation | Chromatin remodeling defects and transcriptional dysregulation | Histone modification / chromatin regulation | Contribute to biologic differences between UTUC and bladder UC | May underlie site-specific pathogenesis and heterogeneity | Potential stratification biomarkers in genomic profiling; investigational therapeutic relevance | (pqac-00000003, pqac-00000010) |
| **HRAS** | Recurrent but less common than FGFR3/TP53 | Activating mutations | MAPK pathway activation | RAS-MAPK | More often associated with non–muscle-invasive pathways in classic urothelial models | Supports proliferative signaling | Primarily biologic marker; potential eligibility for future RAS-pathway strategies | (pqac-00000009, pqac-00000011) |
| **ERBB2 (HER2)** | Overexpression / activation in subset; exact % not given in available contexts | Amplification/overexpression, mutation in subset | Enhanced proliferation, invasion, metastasis signaling | ERBB/HER2 RTK signaling | More often discussed in advanced/aggressive disease workups | Linked to invasion and metastasis in review literature | Candidate biomarker for HER2-directed therapy trials and precision oncology approaches | (pqac-00000009, pqac-00000012) |
| **PTEN** | Recurrent but less common than TP53/FGFR3 | Loss-of-function mutation/deletion | Reduced negative regulation of PI3K signaling | PI3K-AKT-mTOR | More relevant in invasive/aggressive molecular programs | May contribute to progression and therapy resistance | Supports rationale for PI3K/AKT/mTOR combination strategies | (pqac-00000009, pqac-00000011) |
| **DDR gene group (e.g., BRCA1, CHEK2, PMS2 and related genes)** | Pathogenic germline variants found in ~11.24% of one Chinese UC cohort; deleterious DDR alterations in ~22.9% UTUC and ~33.9% UCB | Germline or somatic pathogenic variants | Impaired homologous recombination / checkpoint repair | DNA damage response / repair | Present in both UTUC and bladder UC, with prevalence differences by site | May raise mutational burden and treatment sensitivity | Potential relevance to platinum response, immunotherapy response, and future PARP-based strategies; also germline counseling implications | (pqac-00000010) |
| **APOBEC mutational process** | Not a gene alteration but dominant mutational signature; accounted for ~66% of SNVs in TCGA MIBC per review summary | Cytidine deaminase mutational signature | Hypermutation and genomic diversification | Mutagenesis / innate immunity-related editing | Strongly emphasized in MIBC | Associated in review summary with improved 5-year overall survival in MIBC despite high mutation burden | Relevant to biomarker development, immunogenicity, and molecular taxonomy rather than direct targeting | (pqac-00000010) |


*Table: This table summarizes recurrent molecular alterations in transitional cell carcinoma/urothelial carcinoma, emphasizing stage associations, pathway biology, prognostic patterns, and current or emerging therapeutic relevance. It is useful for linking disease mechanisms to precision oncology and biomarker-driven management.*