A Myc transcriptional program that is independent of EMT drives a poor prognosis tumor-propagating phenotype in HER2+ breast cancer

The HER2 (ERBB2) and MYC genes are commonly amplified genes in breast cancer, yet little is known about their molecular and clinical interaction. Using a novel chimeric mammary transgenic approach and in vitro models, we demonstrate markedly increased self renewal and tumour propagating capability of cells transformed with Her2 and c-Myc. Co-expression of both oncogenes in cultured cells led to a pronounced activation of a c-Myc transcriptional signature and acquisition of a self renewing phenotype independent of an EMT programme or regulation of cancer stem cell markers. We show that HER2 and c-MYC are frequently co-amplified in a clinical breast cancer cohort and that co-amplification is strongly associated with aggressive clinical behaviour and poor outcome. Lastly, we show that in patients receiving adjuvant chemotherapy (but not targeted anti-HER2 therapy), MYC amplification is associated with a poor outcome in HER2+ breast cancer patients. These findings demonstrate the importance of molecular context in oncogenic transformation and acquisition of a malignant stem-like phenotype and have important diagnostic and therapeutic consequences for the clinical management of HER2+ breast cancer. Gene expression analysis of Her2, Myc, and Her2 + Myc over expression on MCF10A cells, with MCF10A vector control comparison