Emerging Role of Tumor-associated Macrophages as Therapeutic Targets in Glioblastoma Multiforme

The most common types of primary brain tumors in adults are gliomas. Glioblastoma multiforme (GBM) is the most highly aggressive type of glioma. GBM contains various numbers of cells with characteristics of activated or dysmorphic macrophages/microglia. Among them, some cell types provide significant support for tumor growth, while others are able to inhibit tumor progression. These cells are generally considered part of the tumor stroma and are often described as TAMs (tumourassociated macrophages). The presence of TAMs has been linked to increased tumor grade and poor clinical outcome in GBM, suggesting that depletion or inhibition of these cells may suppress tumor growth. A better understanding of tumor microenvironment in the brain would therefore be expected to contribute to the development of improved therapies for brain tumors that are urgently required due to a poor availability of treatments for these malignancies. This review summarizes some of the known interactions between brain tumors and different stromal cells, and also discusses potential therapeutic approaches within this context.