MYC is amplified in BRCA1-associated breast cancers.

Purpose: Germ-line mutations in the BRCA1 tumor suppressor gene predispose to early onset breast cancers with a distinct phenotype characterized by high tumor grade, aneuploidy, high proliferation rate, and estrogen receptor-negativity. The molecular mechanisms and cooperative oncogenes contributing to multistep tumor progression in cells lacking BRCA1 are not well defined. To examine whether C-MYC (MYC), a transforming oncogene associated with genetic instability, contributes to multistep tumor progression in BRCA1-associated breast cancer, we have analyzed tumors from women with hereditary BRCA1-mutated and sporadic breast cancers.