PGR and carcinoma: Consequently, RA inhibits the growth of carcinoma cells in which the CRABP2/FABP5 ratio is high such as MCF-7 mammary carcinoma cells [22, 25, 26, 38, 39] but promotes oncogenic activities in carcinomas where this ratio is low such as in the triple-negative MDA-MB-231, breast cancer cells which lack estrogen receptors, progesterone receptors and the receptor tyrosine-protein kinase erbB-2 (ERBB2) [17, 40, 41].