In addition, when a panel of 47 human breast cancer and immortalized breast cell lines grown in vitro were treated with a CDK4/6 inhibitor (palbociclib), sensitive cell lines (estrogen receptor positive) showed increased expression of the genes RB1 and CCND1 and reduced expression of CDKN2A (p16) [11]. The gene discussed is CCND1; the disease is breast cancer.