PIK3CA and breast cancer: Dysregulation of the PI3K/AKT pathway has an impact on resistance to chemotherapy, endocrine therapy, HER2− targeted therapy, PARP inhibitors, and immunotherapy in breast cancer, and blockage of this pathway can enhance drug sensitivity and reverse resistance (Miller et al., 2011a; Hu et al., 2015; Pernas and Tolaney, 2019).