PIK3CA and breast cancer: Further, Shishido et al. conducted sequential mutational analysis of five ERBB2-mutated breast cancer patients treated with neratinib and also showed new mutations arising in ERBB2, PIK3CA, and TP53 in a patient with treatment failure [25] In this cohort HER2-targeted treatment resulted in an overall response rate of 37%, a disease control rate of 68%, and a median progression-free survival (PFS) of 4.4 months.