Prognostic value of PIK3CA mutations in HER2-positive early stage breast cancer: A French cohort study.

e11607 Background: Breast cancer (BC) is a heterogeneous disease with different prognostic according to molecular characteristics. About 15% of breast cancers have erbb2 oncogene (HER2+) overexpression or amplification. Experimental and clinical data suggest that mutational activation of the PIK3 pathway could confer resistance to HER2 targeted therapies. In the adjuvant setting, the prognostic value of PIK3CA mutations is unclear with conflicting results (Loibl, S., et al. J Clin Oncol. 2014,32(29): p. 3212-20; Baselga, J., et al. J Clin Oncol. 2014,32(33): p. 3753-61; Majewski, I.J., et al. J Clin Oncol. 2015; Esteva, F.J., et al. Am J Pathol. 2010,177(4): p. 1647-56; Loi, S., et al. J Natl Cancer Inst. 2013,105(13): p. 960-7.) Our study aims was to determine the impact of mutated PIK3CA gene on HER2+BC outcome treated with adjuvant chemotherapy with or without trastuzumab. Methods: Between 1998 and 2012, we identified 180 patients with HER2+ early breast cancer treated in the adjuvant setting at our ce...