Abstract
BACKGROUND: Brain metastases (BMs) derived from gastrointestinal (GI) cancers (GIBMs) are associated with a poor prognosis, necessitating reliable prognostic indicators. While tumor-infiltrating B cells (TIBs) and tissue-resident memory T cells (TRMs) contribute to antitumor immunity, their prognostic relevance in GIBMs remains unclear. This study aimed to investigate the prognostic significance and spatial distribution of TIBs and TRMs in surgically resected GIBMs. METHODS: Retrospective histopathological analyses were conducted on 13 surgically resected GIBM tissues. Densities of TIBs, CD4+ T cells, CD8+CD103+ TRMs, and CD8+CD103- non-TRMs were quantified via immunohistochemistry and digital image analysis. Their spatial distributions relative to tumor vessels were also assessed. These immune cell densities were then correlated with clinical parameters and overall survival (OS), including the Graded Prognostic Assessment (GPA). RESULTS: TIBs and CD4+ T cells predominantly accumulated perivascularly in the tumor stroma, forming lymphocyte clusters without mature tertiary lymphoid structure (TLS) characteristics. TRMs, conversely, demonstrated deeper infiltration into the tumor epithelium than non-TRMs. Importantly, higher TIB density significantly correlated with GPA-predicted survival and improved OS after BM diagnosis and BM surgery. Furthermore, increased TRM density also significantly correlated with enhanced OS after BM diagnosis. Other T cell subsets did not show consistent survival correlations. CONCLUSIONS: Quantifying TIB and TRM densities in resected GIBM tissues can serve as reliable prognostic indicators for patient survival. These findings provide crucial insights into the BM immune microenvironment, supporting the development of novel immunotherapeutic strategies for this challenging disease.