CDKN2A and cancer: Further studies are warranted to determine the basis for the nuclear accumulation of p21 at late times (7 days) after irradiation in some cancer cell lines that express mutant p53 and to elucidate the reason why some p53-mutated cell lines (e.g., MDA-MB-453 s and SKMEL-24, but not ABC-1 and HCC44) exhibit the delayed nuclear accumulation of p21 after irradiation but not of p16.