Tumor-associated macrophages in feline meningiomas: Exploring their prognostic significance

Tumor-associated macrophages (TAMs) are the predominant immune cells in the tumor microenvironment (TME) of human meningiomas. They exhibit different functional phenotypes that contribute either to an anti-inflammatory and anti-tumor response (M1 phenotype), or an immunosuppressive and pro-tumor response (M2 phenotype). In meningiomas of cats, the specific role of TAMs in determining prognosis and post-surgery outcome remains unclear. This study aimed to characterize the macrophage population in feline meningiomas, differentiate M1 from M2 phenotype, and investigate the relationship of the results to prognosis. Fifty-seven surgically removed feline meningiomas were studied. Immunolabeling was performed on formalin-fixed paraffin embedded samples with primary antibodies anti-MAC387 (M1 macrophage), CD163 and CD204 (M2 macrophage), Iba1 (pan-macrophage), and Ki67. The cells in all cases expressed Iba1 and CD163, while MAC387 and CD204-expression varied. Moreover, macrophages were more numerous in high-grade tumors across both M1 and M2 phenotypes. Although none of the markers were predictive of recurrence on Cox models (P > .05), based on the significant association between M2 CD163-positive macrophages and high-grade tumors, and their shorter post-surgery recurrence-free times, the results suggest that M2 macrophages might play a role in the behavior and prognosis of feline meningiomas.