Differential expression of BRCC2, a novel BH3-like domain-containing apoptotic molecule, in ductal versus lobular breast carcinoma

Abstract

Background: BRCC2 (breast cancer cell 2) gene was discovered as an approximately 1.2 kb transcript in MDA-MB 231 human breast cancer cells (GenBank accession numbers AF220061 and AF303179). BRCC2 is a 12 kDa cytosolic protein containing a BH3-like domain at the N-terminus (Broustas et al., J. Biol. Chem., 279: 26780, 2004). The exogenous expression of BRCC2 causes activation of caspase-9, caspase-3 and apoptosis in cancer cells. This study was designed to evaluate the relative expression of BRCC2 in breast tumor tissues vs. adjacent/matched benign breast epithelium and in ductal carcinoma vs. lobular phenotypes.

Clinical specimens and methods: Formalin-fixed, paraffin-embedded tissue sections from a total of 121 cases of invasive ductal carcinoma (IDC) and/or invasive lobular carcinoma (ILC) were analyzed by the standardized manual or automated IHC assay using a custom generated BRCC2 antibody. The archival breast tissues from thirty-nine cases (31 IDC, 5 ILC, and 3 IDC and ILC) were obtained from the Human Tumor Bank at the Georgetown University Hospital (GUH). Additionally, representative archival tissue blocks were also obtained from eighty-two cases (50 IDC and 32 ILC) from the Albany Medical College (AMC). The malignant/benign breast epithelium was semiquantitatively scored for BRCC2 immunoreactivity in all cases based on both intensity of staining and percentage of positive cells.

Results: An essentially cytoplasmic pattern of BRCC2 protein expression was observed to varying degrees in both the benign epithelial elements and invasive tumors. Cytoplasmic BRCC2 immunoreactivity was reduced or absent in most IDCs as compared to the benign epithelium and ILCs. In the GUH cohort, decreased BRCC2 expression was noted in 30/34 IDC (88.24%) as compared to matched/adjacent benign elements (p < 0.0001, one-sided exact binomial test of P0 = 0.5). In 8/8 ILC, BRCC2 expression was equal to or higher than the matched benign tissue (p < 0.004, one-sided exact binomial test of P0 = 0.5). Differential expression of BRCC2 in IDCs versus ILCs was also significant (p < 0.004, Fisher's exact test). In the AMC cohort, similar decreased BRCC2 expression was noted in 22/50 IDC (44%) as compared to its’ expression in 32/32 ILC (100%) (p = 0.0000, Pearson’s chi-square test).

Conclusions: We conclude that BRCC2 expression is significantly lost or decreased in a subset of infiltrating ductal carcinomas and that this marker appears to be of noteworthy diagnostic utility in the histological differentiation of ductal and lobular carcinomas.