RARA and breast carcinoma: For instance, in breast cancer cells treated with ligands specific for PPARγ and RXR/RAR, troglitazone and 9-cis-retinoic acid, respectively, a reduction in proliferation was observed,58 and low doses of PPARγ and RXR ligands also promoted apoptosis.59 This suggests that RXRs have an anti-tumorigenic role, potentially through heterodimer formation with PPARγ.