BMRK-09 Prognostic Role of Tumor-Infiltrating Lymphocytes and Tertiary Lymphoid Structures in Brain Metastasis

Abstract Brain metastases (BrMs) constitute the most common type of brain cancer with abysmal prognosis. Given the high incidence and poor prognosis of BrM, understanding the tumor microenvironment (TME) architecture across BrM subtypes is increasingly crucial, especially with the emergence of novel immunotherapeutic agents like immune checkpoint inhibitors, which have demonstrated efficacy in melanoma and lung cancer BrM. Tertiary lymphoid structures (TLS) are spatially organized lymphoid aggregates in the TME that mediate antitumor immunity. Despite being established as prognostic and predictive markers in various cancers, their significance in BrM lacks extensive investigation. We performed gene expression profiling using paired-end RNA sequencing and multiplex immunofluorescence combined with spatial imaging on 149 human BrM samples. Cell type deconvolution analysis revealed that BrMs from non-small cell lung carcinoma (NSCLC) and malignant melanoma exhibited significantly higher immune cell infiltration compared to BrMs from breast carcinoma. Furthermore, B cell infiltration was detected in some patients, suggesting potential TLS formation. We created a metagene signature comprising TLS hallmarks in BrMs using transcriptomic profiling, allowing us to categorize BrM patients into TLS-positive and TLS-negative groups. This finding was corroborated by multiplex immunofluorescence staining of corresponding BrM tissue sections, which confirmed TLS-like aggregate formation in 40% of the BrM patients. Differential gene expression analysis highlighted the presence of activated lymphocyte-mediated immunity as well as increased immunoglobulin production signature in TLS-positive tumors. Additionally, a higher TLS signature score was associated with improved overall survival of lung carcinoma patients after BrM diagnosis. Our results underscore the heterogeneity of the tumor microenvironment in BrM, and the identification of intratumoral TLS may guide patient stratification for therapeutic interventions.