PIK3CA and breast cancer: To determine whether PI3K/AKT/mTOR inhibition activates STAT3 in different PTEN-deficient cancer cells, we treated the gastric cancer cell line HGC-27, breast cancer cell lines MDA-MB468 and MDA-MB436, renal cell carcinoma cell line 786-O, and melanoma cell lines U-251 and U-87 with the AKT kinase inhibitor MK2206.