A 28-year-old woman with BRCA1 germline mutation is found to have a breast carcinoma. The typical histological subtype enriched in BRCA1-mutant breast cancers and its IHC profile is:
- A ER+/PR+/HER2+ luminal B-like carcinoma with grade 2 histology
- B HER2-enriched subtype with grade 3 histology and ER−
- C Triple-negative breast carcinoma (ER−/PR−/HER2−), high grade, often with medullary-like or metaplastic features ✓
- D Lobular carcinoma with E-cadherin loss — strongly associated with BRCA1
Correct answer: C. Triple-negative breast carcinoma (ER−/PR−/HER2−), high grade, often with medullary-like or metaplastic features
Explanation
BRCA1-associated breast cancers are strongly enriched for the basal-like molecular subtype, which corresponds to triple-negative carcinoma (ER−, PR−, HER2−) on clinical IHC. They show high grade (grade 3), pushing margins, lymphocytic infiltrate, central necrosis, and often medullary-like or metaplastic histology. Basal markers (CK5/6, CK14, EGFR, p63) are expressed. BRCA2 mutations are more associated with ER+ luminal carcinomas. CDH1 (E-cadherin) loss characterizes lobular carcinoma and is NOT associated with BRCA1.
Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.
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