Amplification of TOP2A and HER-2 genes in breast cancers occurring in patients harbouring BRCA1 germline mutations

Abstract

BRCA1 associated tumours are found to express an oestrogen receptor negative “basal epithelial-like” phenotype. In contrast to ER negative tumours in general, such tumours rarely harbour amplification of the HER-2 gene. However, little is known about TOP2A gene amplification status in BRCA1-associated tumours. Such information may be of importance to therapy, as amplification of TOP2A has been associated with dose-dependent sensitivity to anthracycline therapy in breast cancer.

We examined 40 breast carcinomas from BRCA1 mutation carriers and 40 sporadic breast carcinomas matched for age, tumour diameter and histological grade for HER-2 and TOP2A amplification status using fluorescence in situ hybridisation (FISH). Co-amplification of TOP2A and HER-2 was found in four of the mutation carriers and in three of the controls. While six tumours in the control group harboured HER-2 amplifications with normal TOP2A, this occurred in three of the BRCA1 associated tumours only. In contrast, three of the BRCA1-associated tumours but none of the controls harboured TOP2A amplification despite normal HER-2 status. Our findings have potential therapeutic implications. HER-2 assessment is routinely used to select breast cancer patients for trastuzumab but also dose-intensive anthracycline therapy. Our data suggest that BRCA1-associated breast cancers also need to be tested for TOP2A amplification.