MYC and cancer: Furthermore, calcitriol inhibited the expression of c-Myc and cyclin A, D1 and D2, all involved in the control of cell cycle (22, 24, 30, 49), in keeping with its ability to suppress the expression of c-Myc-regulated genes and to promote cell cycle arrest and inhibition of cyclins in both normal and cancer cells (30, 50, 51).