CDKN2A and cancer: Finally, we examined the presence of distinct E2F1 activity in a panel of 33 cancer cell lines and five normal growing cell types (Table 1), available in our laboratory, utilizing the E2F response elements of the ARF (EREA) and TAp73 (ERE73) genes, which specifically respond to distinct E2F1 activity, and the corresponding E2F1 binding site mutants.