To further elucidate the role of deregulated E2F activity in the elevated cancer cell specificity of ERE73 (1 + 2)-ARF (−13) and ERE73 (3 + 4)-ARF (−13), we examined whether repression of E2F activity by PSM.7-LP, a constitutively active form of pRB, could diminish the cancer cell-specific activity of both ERE73s-ARF constructs. The gene discussed is RB1; the disease is cancer.