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Tumor-associated macrophages (TAMs) are the multifarious groups of cells that originate mainly from the peritumoral tissue or bone marrow and can be divided into two main types: M1 and M2. Among them are the infiltration of M1 tumor-associated macrophages in the early stages of tumorigenesis, which can secrete proinflammatory cytokines and turn in inhibit tumor growth. On the contrary, M2 tumor-associated macrophages are predominant in the late stage of tumor formation. Type II cytokines, which are secreted by them, can promote anti-inflammatory reaction and thus promote tumor growth. However, it remains unclear when M1 tumor-associated macrophages will be transformed to M2 tumor-associated macrophages, but tumor hypoxia is currently thought to be associated with such a shift. M2 tumor-associated macrophages secrete many proteases such as cathepsin, cytokines, and an epidermal growth factor. It is making the tumor-prone to growth, angiogenesis, which in turn violates other tissues.

Clinically, taking breast cancer as an example, in 128 patients in the first or second stage, it was found that more patients with M2 tumor-associated macrophages had a higher degree of histology, more angiogenesis, and worse overall survival M1 tumor-associated macrophages more, then just the opposite.

Macrophage is the common cells in breast tumors. It has a profound effect on the immune status of tumor tissues. Without disease, macrophages action as superior phagocytes for the body. Specifically killing and eliminating cells that are thought to be a threat. They represent the first line of protection and the bridge of connecting the intrinsic and adaptive of the immune system. However, the large number of tumor and the derived factors present within TME act to destroy the tumoricidal activity function of macrophages. Exposure to TME provides hypoxic conditions, growth factors and immunosuppressive cytokines that confer trophic macrophages to tumor-associated macrophages (TAM). These features promote tissue growth and repair and are an integral part of development so that macrophages within breast tumors are inadvertently authorized to promote tumor growth and metastasis.