Evita Weagel, Curren Smith, Ping Guo Liu, Richard Robison and Kim O’Neill
The immune system plays an important role in the development of, and progression of cancer. Macrophages exhibit a variety of responses according to varying stimuli, and express different functions depending upon the microenvironment surrounding them. Macrophages can be pro-inflammatory (M1) or anti-inflammatory (M2). Research studies have shown that infiltration of macrophages can account for >50% of the tumor mass in some cancers, aid in metastasis by inducing angiogenesis, and signify a poor prognosis. Macrophages that migrate to the tumor site, remain there, and aid in angiogenesis and metastasis are termed tumor associated macrophages (TAMs) and are thought to express an M2 phenotype. This review will examine the polarization states of macrophages, their functions and role in cancer, their activation pathways and metabolism, and potential approaches to cancer immunotherapies using macrophages.