PIK3CA and breast cancer: Likewise, resistance to anti-EGFR and anti-HER2 therapies are associated with PI3K pathway activation by PIK3CA mutations in EGFR mutant LADC [9], and HER2-positive breast cancer [10] [11], or by loss of PTEN [12] or HER3 activation (which activates the PI3K pathway) in breast cancer models [13].