Macrophages represent a heterogenous cell population in the tumor microenvironment and their proximity to tumor or stromal elements are widely studied. Tumor-associated macrophages (TAMs) are associated with tumor growth, poor prognosis, and metastasis. There are 2 main macrophage phenotypes: the classically activated M1 phenotype and the alternatively activated M2 phenotype. Most M2 macrophages are considered to be TAMs and function to promote tumor angiogenesis and metastasis. CD163 is a marker of M2 macrophages and is expressed on the cell surface of human monocytes and macrophages that evolve predominantly in the late phase of inflammation.