Loss of heterozygosity at the BRCA2 locus detected by multiplex ligation-dependent probe amplification is common in prostate cancers from men with a germline BRCA2 mutation.

PURPOSE: Prostate cancer risk is increased for men carrying a pathogenic germline mutation in BRCA2, and perhaps BRCA1. Our primary aim was to test for loss of heterozygosity (LOH) at the locus of the mutation in prostate cancers from men who a carry pathogenic germline mutation in BRCA1 or BRCA2, and to assess clinical and pathologic features of these tumors. EXPERIMENTAL DESIGN: From 1,243 kConFab families: (a) 215 families carried a pathogenic BRCA1 mutation, whereas 188 families carried a pathogenic BRCA2 mutation; (b) of the 158 men diagnosed with prostate cancer (from 137 families), 8 were confirmed to carry the family-specific BRCA1 mutation, whereas 20 were confirmed to carry the family-specific BRCA2 mutation; and (c) 10 cases were eliminated from analysis because no archival material was available. The final cohort comprised 4 and 14 men with a BRCA1 and BRCA2 mutation, respectively. We examined LOH at the BRCA1 and BRCA2 genes using multiplex ligation-dependent probe amplification of DNA from microdissected tumor. RESULTS: LOH at BRCA2 was observed in 10 of 14 tumors from BRCA2 mutation carriers (71%), whereas no LOH at BRCA1 was observed in four tumors from BRCA1 mutation carriers (P = 0.02). Under the assumption that LOH occurs only because the cancer was caused by the germline mutation, carriers of BRCA2 mutations are at 3.5-fold (95% confidence interval, 1.8-12) increased risk of prostate cancer. A high Gleason was the only distinct clinical feature. CONCLUSIONS: These observations are consistent with the idea that BRCA2, but not BRCA1, is a tumor suppressor of prostate cancer.

Aberrant luminal progenitors as the candidate target population for basal tumor development in BRCA1 mutation carriers.

Basal-like breast cancers arising in women carrying mutations in the BRCA1 gene, encoding the tumor suppressor protein BRCA1, are thought to develop from the mammary stem cell. To explore early cellular changes that occur in BRCA1 mutation carriers, we have prospectively isolated distinct epithelial subpopulations from normal mammary tissue and preneoplastic specimens from individuals heterozygous for a BRCA1 mutation. We describe three epithelial subsets including basal stem/progenitor, luminal progenitor and mature luminal cells. Unexpectedly, we found that breast tissue from BRCA1 mutation carriers harbors an expanded luminal progenitor population that shows factor-independent growth in vitro. Moreover, gene expression profiling revealed that breast tissue heterozygous for a BRCA1 mutation and basal breast tumors were more similar to normal luminal progenitor cells than any other subset, including the stem cell-enriched population. The c-KIT tyrosine kinase receptor (encoded by KIT) emerged as a key marker of luminal progenitor cells and was more highly expressed in BRCA1-associated preneoplastic tissue and tumors. Our findings suggest that an aberrant luminal progenitor population is a target for transformation in BRCA1-associated basal tumors .