ESR1 and breast cancer: Notably, missense mutations in PIK3CA were illustrated in a mutually exclusive pattern with other somatic alterations in its up‐ and down‐stream molecules, including EGFR, ERBB2, ERBB3, FGFR2, FGFR3, FGFR4, AKT1, AKT3 and ESR1 in HER2+ breast cancer (Figure 1D).