Effect of somatic mutations in the four genes of the HER family on occurrence in HER2-positive breast cancer, cell proliferation rates, and resistance to HER2-targeted therapies in vitro.

615 Background: Somatic mutations in the 4 HER family genes (EGFR, HER2, 3, 4) occur in HER2-positive breast cancer (HER2+ BC). (Cancer Genome Atlas N. Comprehensive molecular portraits of human breast tumors. Nature 2012;490(7418): 61-70.) We investigated their frequency in a large set of HER2+ BCs and their therapeutic relevance. Methods: Tumors from 246 HER2+ BC patients who received adjuvant trastuzumab-based therapy after surgery were reviewed by a pathologist for tumor content. DNA from 48 matched normal and cancerous samples was sequenced using the Agilent kinome library and a MiSeq. Somatic HER gene mutations identified in this way had their frequency determined by Sequenom MassArray (n=246). HER gene mutations were correlated with patient outcomes. Constructs of 2 hotspot HER3/4 mutations were created and transfected into BT474, HCC1569 and HCC1954 cells. Doubling time, proliferation, Boyden chamber assays and RPPA were used to determine effects of mutations on cell growth, invasion, signalling a...