CDKN1A and leukemia: TMPyP4 shows anti-tumor activity in several tumor cells, including (1) retinoblastoma cell lines, by inducing p53 expression and activating p38 in the MAPK–JNK–ERK signaling pathway [161]; (2) leukemia cell lines, by reducing c-myc expression and promoting the p21CIP1 and p57KIP2 proteins to activate p38 [160]; (3) prostate carcinomas, by downregulating c-myc expression and inhibiting telomerase activity [159]; (4) melanoma cells, by decreasing RAS expression in the ERK pathway [10].