Tumor-Associated Macrophages in Breast Cancer

Neoplastic cells form only one part of a complex network of cell types that make up a breast tumor. The normal cell types that make up the nonneoplastic components of tumors include fibroblasts, endothelium, and inflammatory cells, such as tumor associated macrophages (TAMs). TAMs have the potential to carry out both anti- and protumor activities. In their antitumor role TAMs can present tumor antigens to cytotoxic T-cells and are capable of being directly cytotoxic to neoplastic cells. Conversely, TAMs are also able to promote tumor growth directly by secreting breast tumor mitogens, such as epidermal growth factor, and indirectly by stimulating tumor angiogenesis and metastasis. Recent studies have indicated that in breast cancers the protumor role of TAMs is dominant, and that TAMs may be executing a “wound healing” type of process in response to stimuli found in the tumor microenvironment, such as hypoxia. As such, TAMs may provide opportunities for future therapeutic interventions.