CDKN1B and cancer: As shown in Figure 2, breast (A and C, left panel) and glioblastoma (B and D, left panel) cancer cells synchronized by serum starvation increased their expression of p27 by 6 to 24 h, whereas expression of cyclin D1 showed a progressive reduction in breast cancer cells (Fig. 2A, left panel) and a rather stable level of expression in glioblastoma cells (Fig. 2B, left panel).