A Pilot Study on BRCA1/2 and PI3K Mutations Across Subtypes of Triple Negative Breast Cancer in North Indian Population.

Abstract

BRCA1/2 are tumor suppressor genes which regulate the DNA repair mechanism. Mutations in BRCA1/2 may increase the risk of breast cancer in patients. In the present study frequency of BRCA1/2 mutations in triple negative breast cancer (TNBC) patients was assessed and correlated with molecular subtypes of TNBC. Blood samples from 65 confirmed cases of TNBC were collected. DNA was isolated from whole blood and libraries were prepared using a BRCA1/2 custom panel. Sequencing was done on Ion torrent S5 sequencer and ion reporter was used for data analysis. Further molecular subtyping of mutation positive TNBC cases was done using immunohistochemistry markers CK5/6; CK4/14; Vimentin and E-Cadherin and androgen receptor (AR) using tissue microarray. Twenty five of 65 patients had heterozygous pathogenic mutations, alterations with conflicting interpretation of pathogenicity, variants of uncertain significance and variants of unknown significance. Nine patients had pathogenic mutation in BRCA 1 gene only and 2 patients had pathogenic mutations in BRCA2 gene. Two patients were transheterozygous for BRCA mutations, that is, had pathogenic mutations in both BRCA1/2 genes simultaneously and 5 were compound heterozygous (involving BRCA2 gene in all the cases). Prevalent subtypes among BRCA positive cases were unclassified subtype (n=4, 33%), Basal like (n=5, 41%), and mesenchymal subtype (n=3, 25%). None of the LAR subtype showed BRCA1/2 mutations. The present study observed that the BRCA1 mutation is more frequent than BRCA2 mutation in TNBC. BRCA1/2 mutations do not correspond to BRCAness or basal phenotype. Considering high incidence of breast cancer and lack of correlation of basal morphology with BRCA1/2 mutation, the molecular methods should be used for screening for BRCA1/2 mutations. This will not only help in familial screening but also in deciding targeted therapy with PARP (poly-ADP ribose polymerase) inhibitors.