Macklis et al (1992) demonstrated that α-particle radioimmunotherapy can induce apoptosis in murine lymphoma cells. Using the 213Bi-PAI2 conjugate, we have also demonstrated that 213Bi-PAI2 can induce a high percentage of TUNEL-positive PC3 prostate cancer cells in vitro and in vivo (Li et al, 2002b). These data suggest that apoptosis may be the lethal pathway of 213Bi-PAI2 therapy for MDA-MB-231 breast cancer cells. The gene discussed is SERPINB2; the disease is breast cancer.