We summarised studies on response to TKI treatment of HER2-positive breast cancers according to PIK3CA mutation status (Supplementary Table S5), almost all the previous studies explored the association of PIK3CA mutations and resistance to lapatinib, while evidence for pyrotinib, a new pan-ErbB TKI with the capacity to irreversibly block ErbB1, ErbB2 and ErbB4, was absent. The gene discussed is ERBB4; the disease is breast cancer.