CDKN1B and cancer: Previous papers have demonstrated that rapamycin induces the inhibition of cell proliferation and G1 arrest possibly due to downregulation of the expressions of cyclin D1 and c-myc, and upregulation of the expressions of p21Cip1 and p27Kip1 through rapamycin-induced mTOR inhibition in various cancer cells, including MCF-7 cells [5,6].