IL4 and neoplasm: The initial idea about mononuclear phagocyte heterogeneity (a concept known since the 90s) was based on a simple binary division: M1 (or classically activated) macrophages stimulated by bacterial components (e.g., LPS or other TLR ligands) and cytokines such as IFNs have inflammatory immunostimulatory functions and anti-tumor activity, while M2 (or alternatively activated) macrophages stimulated by cytokines such as IL-4 and IL-10, have immunosuppressive, anti-inflammatory functions and favor tumor progression.