CXCL8 and breast carcinoma: Several studies have shown that in breast cancer cell lines, invasion is directly proportional to IL-8 expression [299] where, various cytokines, such as IL-1β, TNFα, and IL-6, as well as hormones, such as progesterone and estrogen, are thought to up-regulate IL-8 expression in breast cancer cells compared to normal breast tissue [300].