There are many such observed issues in breast cancer, for example, the co-existence of mutations of PIK3CA and amplification of ERBB2 have been linked with resistance to HER2-targeting drugs lapatinib and trastuzumab (Fontanella et al., 2014), which provides the rationale of combining HER2 and PI3K inhibitors in different clinical trials. Here, PIK3CA is linked to breast cancer.