Tumor-associated macrophages: a novel potential target for cancer treatment.

Special emphasis about cancer metastasis was concentrated on tumor cells themselves, and we usually considered the ability of migration and invasion was the final decider. Recently, bewaring of tumor microenvironment is a fundamental determinant in metastasis has become the most outstanding breakthrough. Considerable "microbes" in the microenvironment are closely linked with tumor metastatic behaviors, and the major proportion of them is tumor-associated macrophages (TAMs). Actually, TAMs conserve immediate "cross-talk" with cancer cells throughout tumor development. It is generally accepted that TAMs have mostly pro-tumoral functions and play an important role in several stages of tumor progression. This progression involves a series of events that leads from the primary site to the metastatic site, including tumor cell growth, angiogenesis, migration, invasion, intravasation and finally extravasation at distant site where the process begins again (metastasis). Thereby, TAMs has attracted substantial attentions in recent years and could become a promising therapeutic strategy. In this review, we focus on the multi-functions of TAMs in cancer and certain drugs targeting TAMs for cancer treatment those are under experimental research procedures or have even been entered human clinical tests.