Abstract P4-05-15: Breast cancers with BRCA1 and BRCA2 mutations are associated with specific pathologic features and molecular profiles: Results from a TCGA sub-analysis

Abstract

Abstract Background: Previous studies have found that particular pathologic features are more common in breast cancers arising in BRCA mutation carriers. However, the biologic and molecular bases for the morphologic associations are not clear. This study is conducted to analyze pathologic and molecular features in tumors stratified by BRCA1 or BRCA2 mutation status using the breast cancer samples that have comprehensive molecular portraits characterized by the Cancer Genome Atlas (TCGA). Methods: The digital slides of breast cancer samples submitted for comprehensive molecular profiling to the TCGA were reviewed by expert breast pathologists, who were unaware of the BRCA status or other molecular signatures. Each tumor was evaluated and scored for histologic type, nuclear pleomorphism, tubule formation, mitosis, stromal inflammation, and necrosis. 562 cases had both pathology and tumor exome sequencing data available and constituted the current study population. We determined the association of somatic BRCA1 and BRCA2 mutation status with pathologic features and molecular characteristics (mutation of PIK3CA and TP53, and molecular subtypes defined by PAM50 mRNA data) using the Fisher exact test for categorical variables and the Wilcoxon test for ordinal variables. Results: Of the 562 tumors, 514 had no BRCA1 or BRCA2 mutation, while 48 (8.5%) of tumors were found to harbor a BRCA1 mutation (n = 16, 3%), BRCA2 mutation (n = 30, 5%), or mutation in both (n = 2, 0.3%). BRCA1 and BRCA2 mutational status showed no significant association with lobular features, tubule formation, nuclear pleomorphism, or stromal inflammation (all p > 0.05), although there was a trend for increased nuclear pleomorphism in BRCA2 mutant cases (p = 0.07). The lack of significant association of BRCA1/2 mutational status with these features may be due to our study's relatively small number of BRCA1/2 mutant cases. Both BRCA1 and BRCA2 mutations were associated with a higher mitotic count (p = 0.03 and 0.04, respectively). BRCA2 mutation showed no association with necrosis (p = 1), while BRCA1 mutation status was associated with increased necrosis (OR = 2.7, p = 0.04). BRCA2 mutation status showed no significant association with PAM50 subtype (p = 0.37), while BRCA1 mutation status was significantly associated with PAM50 molecular subtype (p = 0.005), with the greatest enrichment among Basal-like (7/70 Basal-like with BRCA1 mutation, 10%) and depletion among Luminal-B (0/79 Luminal-B with BRCA1 mutation, 0%). Neither BRCA1 nor BRCA2 mutations were significantly association with PIK3CA mutations (p = 0.39, 0.08, respectively). BRCA2 mutation status was not associated with TP53 mutations (p = 0.65), while BRCA1 mutation status was associated with increased TP53 mutations (OR = 4.0, p = 0.005). Conclusion: Tumors with BRCA1 and BRCA2 alterations are associated with specific pathologic and molecular features. However, there is molecular and morphologic heterogeneity within these cancers. These factors need to be considered when designing algorithms for BRCA testing and targeted therapy in BRCA-related cancers. Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P4-05-15.