Only PIK3CA-mutant cancer cells in which cytoprotective autophagy was induced by BKM120 treatment showed the response to the combined treatment with BKM120 and HCQ, suggesting that autophagy inhibition might display synergism with anti-cancer drugs which induce cytoprotective autophagy, and that other factors such as alterations of protein-protein interaction within cancer cells might affect the induction of cytoprotective autophagy by anti-cancer drugs even in cancer cells with the same gene mutations. Here, PIK3CA is linked to cancer.