Role of tumor-associated macrophages in human malignancies: friend or foe?

Tumor-associated macrophages (TAMs) play a pivotal role in tumor growth in human malignancies. Published studies have analyzed the relationship between TAM infiltration and the prognosis of patients for many human tumors. Most studies reported a positive correlation between TAM density and a poor prognosis. Studies focusing on macrophage phenotypes emphasized the protumor role of M2 anti-inflammatory macrophages in many types of human tumors. However, TAMs influence tumor progression in various ways that depend on differences in tumor sites, histology, and microenvironments. In this review, we summarize the function of TAMs in various human malignancies by reviewing the data provided in studies of TAMs in human malignancies.