ERBB2 and neoplasm: Therefore, we argued that PIK3CA mutation might be a protective factor associated with improved outcome for treatment‐naïve HER2+ patients; while, with the extension of treatment time, PIK3CA wild‐type cells were killed by chemotherapeutic drugs, and the proportion of mutant tumour cells became the dominant clones, which played an important role in anti‐HER2 resistance with the prolongation of treatment endurance.