Pathologic Features and Immunophenotype of Estrogen Receptor-positive Breast Cancers in BRCA1 Mutation Carriers

Although most breast cancers in BRCA1 mutation carriers are estrogen receptor negative (ER-)with a basal-like phenotype, up to one third are ER positive (ER+). Little is known about the characteristics of this subgroup. To address this, we compared histologic and immunophenotypic features of 60 BRCA1-related ER+ breast cancers with those of 85 BRCA1-related ER- cancers and 174 matched ER+ sporadic cancers. ER+ BRCA1-related cancers were significantly less likely than ER- BRCA1-related cancers to be of pure invasive ductal type (P < 0.001) and to be of histologic grade 3 (P < 0.001), and less frequently to have a highmitotic rate (P < 0.001), pushing (or unknown) margins (P < 0.001), a moderate/marked lymphocytic infiltrate (P = 0.003), or geographic necrosis/fibrotic focus (P < 0.001). In addition, ER+ BRCA1-related cancers less often expressed CK5/6 (P < 0.0001), CK14 (P < 0.0001), and epidermal growth factor receptor (P < 0.0001) and more often expressed progesterone receptor (P < 0.0001). In contrast, when compared with ER+ sporadic cancers, ER+ BRCA1-related cancers were significantly more often of invasive ductal type (P = 0.005) and of histologic grade 3 (P = 0.006), more frequently had a high mitotic rate (P = 0.0003), and were more often CK14+ (P = 0.03). On unsupervised cluster analysis, some ER+ BRCA1 cancers clustered more closely with sporadic ER+ cancers, whereas others clustered more closely with ER- BRCA1-related cancers. Nuclear expression levels of poly(ADP) ribose polymerase 1 in ER+ BRCA1-related cancers were similar to those in ER- BRCA1-related cancers but significantly higher than in ER+ sporadic cancers. We conclude that ER+ BRCA1-related breast cancers show several morphologic and immunophenotypic differences from ER+ sporadic breast cancers as well as some similarities to ER- BRCA1-related cancers.