C5 and neoplasm: However, the complement system has also been suggested to have a role in the development of tumor promoting inflammation and the intermediate product of complement activation C5a has been shown to play a tumor-exacerbating role via elevation of T cell suppression effect and CCL-2 production attracting tumor-associated macrophages (TAMs) and favoring M2-like polarization by bone marrow-derived suppressor cells (50, 51).