PIK3CA and breast cancer: In HER+ breast cancer patients, circulating tumor DNA (ctDNA) profiling identified ERBB2, TP53, EGFR, NF1, and SETD2 mutations contributing to trastuzumab resistance; in the same retrospective study, genetic aberrations in TP53, PIK3CA, and DNA damage repair genes were found in HER2-negative BC patients resistant to chemotherapy [184].