Treatment of CEM and HSB cells with DIM caused a blockade of cell-cycle progression at the G1 phase checkpoint, although this effect was not observed in more differentiated T-ALL cell lines (SUP-T1 or Jurkat); DIM (and I3C) also suppressed expression of CCND3, CDK4 and CDK6 cell cycle regulatory proteins in CEM cells. This evidence concerns the gene CDK4 and acute lymphoblastic leukemia.