PIK3CA and breast cancer: We observed that protein expression of AR, ER, PR, and HER2 was significantly downregulated in C3, and HER2 was significantly overexpressed in C2 relative to C1 and C3; we also found that phosphorylation levels of PI3K/AKT/mTOR pathway proteins were significantly upregulated in C3 (e.g., AKT ps473 and downstream of S6 and 4EBP1, etc.), and that cell-cycle proteins B1, E1, and the kinases CDK1 were all significantly upregulated in C3 (Supplementary Figure S1L), and these results suggest that C3 may be associated with aggressiveness, drug resistance and poor prognosis of BC.