Role of tumor-associated macrophages in hematological malignancies

The tumor microenvironment consists of many non-tumor cells such as leukocytes, endothelial cells, and fibroblasts, and phenotypic changes in a tumor microenvironment are believed to be involved in tumor progression and resistance to anticancer treatments. In hematological malignancies, tumor-associated macrophages (TAMs) that have infiltrated lymphoma or leukemia tissues may be involved in tumor progression, and many researchers have studied phenotypic changes in TAMs. This review article summarizes the publications related to TAMs in hematological malignancies, with an emphasis on CD163(+) protumoral TAMs, which seem to be associated with disease progression. Cell-cell interactions between protumoral TAMs and lymphoma or leukemia cells may play an important role in lymphoma or leukemia microenvironments. Although detailed molecular mechanisms of these cell-cell interactions have not yet been clarified, phenotypic characterization of TAMs is thought to be a useful approach for evaluating clinical prognosis. In addition, targeting TAMs may be a new strategy for treating malignant hematological diseases.