## BRCA1 and BRCA2: Homologous Recombination Repair Genes ### Core Function **Key Point:** BRCA1 and BRCA2 are essential components of the homologous recombination (HR) DNA repair pathway. Germline mutations confer high cancer predisposition. ### Correct Statements Analysis | Statement | Accuracy | Rationale | | --- | --- | --- | | HR repair role | ✓ True | Both proteins essential for RAD51-mediated DSB repair | | Cancer risk | ✓ True | Breast ~70%, ovarian ~40% lifetime penetrance | | Chemotherapy sensitivity | ✓ True | Defective HR → platinum sensitivity (BRCAness) | | Tumor phenotype association | ✗ False | **BRCA1 → TNBC; BRCA2 → ER/PR positive** | ### The Critical Error: Tumor Phenotype Reversal **High-Yield:** The statement reverses the established phenotype-genotype correlation: - **BRCA1 mutations** → **Triple-negative breast cancer (TNBC)** — ER/PR/HER2 negative - Mechanism: BRCA1 involved in estrogen receptor regulation - Typically younger age at onset (mean 41–43 years) - More aggressive behavior - **BRCA2 mutations** → **Hormone receptor-positive (ER/PR+) breast cancer** - Often indistinguishable from sporadic breast cancer phenotypically - Slightly older age at onset than BRCA1 **Clinical Pearl:** This distinction is crucial for: - Genetic counseling (BRCA1 carriers: aggressive surveillance, consider risk-reducing surgery earlier) - Treatment planning (TNBC requires chemotherapy; ER+ may benefit from endocrine therapy) - Prognosis estimation ### Why the Other Options Are Correct 1. **HR repair function:** Both BRCA1 and BRCA2 interact with RAD51 and facilitate homologous recombination repair of DSBs. 2. **Cancer risk penetrance:** Well-established epidemiological data from SEER and international registries. 3. **Chemotherapy sensitivity:** BRCA-mutated tumors exhibit "BRCAness" — platinum and PARP inhibitor sensitivity due to HR deficiency.
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