BACKGROUND: Tumor-infiltrating lymphocytes (TILs) and tumor-associated macrophages (TAMs) have increasingly been reported to impact the brain metastatic process of solid tumors. However, data on intra-individual differences between primary tumor and brain metastasis (BM), as well as their correlation with clinical outcome parameters, is scarce. METHODS: We retrospectively identified patients who received resection of the primary tumor and BM between 01/1990 and 10/2022. Density quantification of TAMs (CD68 RESULTS: In total, 104 patients (46.2% female
median age 57.3 years at BM diagnosis) were included: 78/104 (75%) non-small cell lung cancer, 18/104 (17%) breast cancer, 8/104 (8%) renal cell carcinomas. Densities of CD3 DISCUSSION: By utilizing a unique cohort of matched primary tumor and BM tissue samples, we could demonstrate higher TIL densities in primary tumors and higher TAM densities in BM, respectively. Higher cell densities of CD3