Macrophage differentiation and activation states in the tumor microenvironment

Abstract

Macrophages are amongst the most plastic cells of the body, contributing to organogenesis and tissue homeostasis and regulating the balance between pro- and anti-inflammatory reactions. To accommodate these different functions, macrophages are notoriously heterogeneous and are able to adopt different activation states in response to a changing microenvironment. Accumulating evidence exists that macrophages contribute to all phases of the cancer process. These cells are central players in inflammation-associated carcinogenesis, participate in tumor immunosurveillance, and are involved in tumor progression and metastasis. Inside tumors, tumor-associated macrophages (TAM) are confronted with different tumor microenvironments, leading to TAM subsets with distinct activation states and specialized functions. A better refinement of the molecular and functional heterogeneity of tumor-associated macrophages might pave the way for novel cancer therapies that directly target these tumor-supporting cells.