Mutations in PIK3CA occur in approximately 20-30% of HER2-postive breast cancers, and in vitro investigation and clinical trials have shown the benefit of targeting the PI3K/AKT pathway in HER2-positive breast cancer as a way of overcoming trastuzumab and lapatinib resistance in some cases [10, 22, 30]. The gene discussed is PIK3CG; the disease is breast cancer.