Interleukin (IL)-8 contributes to cancer progression through its multiple functions. Its angiogenic effects are well known, but more recently it has been found to be mitogenic for some cancer cells. Many cancer cells constitutively produce IL-8 and also express the IL-8 receptors, CXCR1 and 2 on the cell membrane. It has been established that IL-8 is an autocrine growth factor for a variety of human cancer cells. The mitogenic effects of IL-8 directly stimulate growth of cancer mass, and it may play a critical role for cancer cells to regrow in metastatic sites.