Although the exact mechanism remains unknown (it is suggested that activation of cell death pathways are involved),7 HIV CXCR4 tropism is associated with a lower risk of developing breast cancer.20,21 Conversely, it is also postulated that tumour progression via immune signalling, neo-angiogenesis and the metastatic spread of breast cancer may be induced by concomitant infection with HIV, which is attributed to 17 genes found in both diseases.7 The gene discussed is CXCR4; the disease is breast cancer.