PTEN alterations in sporadic and BRCA1-associated triple negative breast carcinomas

The similarities between sporadic basal-like breast cancer (BLBC) and BRCA1-mutated breast tumours raise the possibility that deregulation of the same pathway may underlie these tumour types. The aim of this study was to determine if PTEN aberrations are characteristic of both BRCA1 tumours and sporadic TN breast carcinomas with low BRCA1 expression, and can thus be used to identify sporadic tumours potentially sensitive to PARP inhibitors. Twelve BRCA1 tumours, 19 non-BRCA familial breast tumours and 71 unselected TN breast carcinomas were screened for PTEN mutations and assessed for PTEN expression and BRCA1 mRNA expression. Loss of PTEN expression was observed in 67% of BRCA1 tumours and more specifically in 89% of TN BRCA1 tumours highlighting the link between PTEN loss and BLBC in the context of germline BRCA1 mutations. Regarding unselected TN tumours, 56% showed PTEN expression loss and 35% displayed low BRCA1 mRNA expression. Unlike familial breast cancers with low BRCA1 mRNA expression, no significant correlation was observed between the loss of PTEN expression and low BRCA1 mRNA expression in this unselected TN tumours panel. Our data suggest that, unlike the germinal context, PTEN and BRCA1 alterations in sporadic TN breast tumours are independent events.