PIK3CA and breast cancer: BC is further classified into several subclasses, characterized by immunohistochemical staining {(e.g., ER, PR, HER2 (ERBB2)}, proliferation marker protein Ki-67 (MKI67), genomic markers (e.g., BRCA1, BRCA2, and PIK3CA), and immunomarkers (e.g., tumor-infiltrating lymphocytes and PD-L1) [8].