Association of Iba1-Positive Macrophages and B7-H3-Positive Tumor Cells with Tumor Growth Kinetics in WHO Grade II Meningioma

Background/Objectives: WHO grade II meningiomas exhibit heterogeneous clinical behavior that cannot be predicted by conventional histology. This study examined the relationship between the tumor immune microenvironment (TIME) and tumor growth kinetics in order to establish a biological basis for more precise risk stratification. Methods: A retrospective cohort of 15 patients was evaluated. Serial preoperative magnetic resonance imaging (MRI) scans were used to calculate the relative growth rate (RGR) and minimize the baseline tumor size. The densities of Iba1-positive macrophages (TAMs) and B7-H3-positive tumor cells were quantified using a deep learning-based image analysis system. Results: Linear correlation analysis showed no significant associations between individual immune components and RGR. However, median-based stratification revealed distinct associations. Tumors with low TAM density or high B7-H3-positive tumor cell density exhibited significantly higher RGR (P = 0.0401). Additionally, a significant inverse relationship was identified between TAM and that of B7-H3-positive tumor cell densities (Spearman’s R = -0.911, P < 0.001). Conclusions: We identified a proliferative "immune-cold" phenotype in WHO grade II meningiomas, which is characterized by low TAM density and high B7-H3-positive tumor cell density. This study extends established molecular frameworks by suggesting that high B7-H3-positive tumor cells proactively contribute to rapid tumor growth. These findings highlight the importance of targeting B7-H3-positive tumor cells when treating malignant meningiomas.