CXCR4 and breast cancer: In particular, Rovito et al. have revealed that rosiglitazone negatively regulates C-X-C chemokine receptor type 4 (CXCR4) expression through the recruitment of the silencing mediator of retinoid and thyroid hormone receptor (SMRT) co-repressor onto a PPRE localized within CXCR4 promoter region, thus reducing breast cancer cell invasion and migration [7].