CDKN2A and cancer: The increased sensitivity of the ERE73 (1 + 2)-ARF (−13) and ERE73 (3 + 4)-ARF (−13) promoter constructs to deregulated E2F activity, together with their unresponsiveness to physiological E2F activity induced by growth stimulation, suggested that they exhibit high promoter activity in cancer cells and low activity in normally growing cells, resulting in enhanced cancer cell specificity.