A separate study detected proviral HIV-1 DNA in three carcinoma cell lines (HEC1A, endometrium; CaSki, cervix; SiHa, uterus) and primary vaginal epithelial cells [45] and noted a preference for X4 integration, since all these cells expressed high amounts of CXCR4 (∼60%) and SDF-1 (a CXCR4 ligand) blocked integration. Here, CXCR4 is linked to carcinoma.