The nondegradable mutant form of IP3R3 enhances the susceptibility of PTEN-deficient or low-PTEN tumor cells to photodynamic therapy through photosensitizer drug-induced Ca2+-mediated cytotoxicity, suggesting that in PTEN-deregulated cancers, preventing the degradation of IP3R3 constitutes a promising therapeutic approach. The gene discussed is PTEN; the disease is cancer.