ERBB2 and breast cancer: PIK3CA mutation frequencies are different among BC subtypes: 34.5-48.3 %, 22.7-42.2 % and 8.3-25.0 % in HR-positive, HER2-positive, and in triple-negative BC, respectively (Martinez-Saez et al., 2020[31]; Stemke-Hale et al., 2008[41]; Xiao et al., 2021[43]).