PIK3CA and breast cancer: Alterations in the HER2-PI3K-AKT pathway, which include expression of an extracellular domain-truncated HER2 (p95HER2), mutation and amplification of PIK3CA, loss of PTEN or INPPB4, and mutation of AKT1, are known to result in a poor response to chemotherapy with trastuzumab or poor outcome for breast cancer patients [4,5].