However, recent studies have shown that there is no good correlation between the PIK3CA or PTEN mutational status and the response of breast cancer cells to the anti-proliferative effect of PI3K inhibitors36–38 indicating that unidentified mechanisms and/or isoform(s) other than p110α modulate the sensitivity of breast cancer cells to PI3K inhibition. The gene discussed is PTEN; the disease is breast cancer.