Previous studies show that atRA inhibits cell proliferation through downregulation of cyclin D1 (CCND1) and upregulation of cyclin-dependent kinase inhibitor 1B (CDKN1B; a.k.a. p27, KIP1) in HEPM cells (Dong et al., 2017) as well as in MCF-7 cells, a human breast cancer cell line (Teixeira and Pratt, 1997). Here, CDKN1B is linked to breast cancer.