CDKN2A and cancer: Because CDKN2A exon-2 located within the true CDR is the essential exon for coding P16INK4A and P14ARF proteins, the above findings indicate that P16INK4A and P14ARF are coinactivated in 87% (96/110) of human cancer cell lines and tissues containing CDKN2A CDR deletion (Figure 1B).