Interestingly, the same combination regimen may not always be effective, even within the same disease, as Elstner et al. reported that only three (MCF-7, MDA-MB-231, and ZR-75-1) of the eight (MCF-7, BT20, BT474, MDA-MB-231, MDA-MB-436, SKBR3, T-47D, ZR-75-1) breast cancer cell lines they evaluated were sensitive to combinations of the PPARγ ligand TRO and RXRα ligand 9-cis retinoic acid. The gene discussed is RXRA; the disease is breast cancer.