Tumor-Associated Macrophages Are Related to Volumetric Growth of Vestibular Schwannomas

Hypothesis: Tumor-associated macrophages contribute to vestibular schwannoma development. Objective: An important clinical problem regarding vestibular schwannoma treatment is their variable growth rate. Tumor biological research can help to clarify this growth rate and may offer targets for therapy. Inflammation is an important biological process involved in the development of many solid tumors. Macrophages are major determinants of intratumoral inflammation. Macrophages can be divided into two groups; the M1- and M2-type macrophages. M2-type macrophages are associated with tumor-promoting processes like angiogenesis, tumor cell growth, and downregulation of the antitumor immune response. Both macrophages and angiogenesis can serve as targets for therapy. CD163 is a specific marker for M2-type macrophages. The goal of this study was to investigate if the expression of CD163 positive macrophages in sporadic vestibular schwannomas is associated with angiogenesis and tumor growth. Methods: CD163 expression in 10 fast-growing vestibular schwannomas was compared with CD163 expression in 10 slow-growing vestibular schwannomas. Tumor growth was determined by comparing preoperative tumor volume measurements on MRI. The relation between macrophage expression and angiogenesis was evaluated by assessing microvessel density (CD31). Results: CD163 expression and microvessel density were significantly higher in fast-growing vestibular schwannomas (p G 0.001 and p = 0.019, respectively). Tumors with higher CD163 expression contained significantly more microvessels (p = 0.014). Conclusion: This study demonstrates that M2-type macrophages in vestibular schwannomas relate to angiogenesis and volumetric tumor growth. These results imply that the M2-type macrophage infiltrate contributes to progressive tumor growth, making it a potential target for pharmacologic therapy.