CDKN1A and cancer: In further supporting p21’s role in cancer cell differentiation, the expression of p21 increases in various human malignant cell lines including lymphoma-derived cell line U937 [104,105,106], p53-null promyelocytic human leukemia (HL) cells HL-60 [107,108,109,110], acute myeloid leukemia (ML) cell lines ML-1, ML-2 and ML-3 [111], megakaryoblastic leukemia cell line CMK [112], epithelial colorectal adenocarcinoma cells Caco-2 [113], neuroblastoma cell line SH-SY5Y [114,115] and chondrosarcoma cells SW1353 [116], sometimes associated with its cytoplasmic localization [63,117].