Immune suppressive microenvironment in brain metastatic non-small cell lung cancer: comprehensive immune microenvironment profiling of brain metastases versus paired primary lung tumors (GASTO 1060).

Lung cancer is one of the most common causes of brain metastases and is always associated with poor prognosis. We investigated the immunophenotypes of primary lung tumors and paired brain metastases, as well as immunophenotypes in the synchronous group (patients with brain metastases upon initial diagnosis) and metachronous group (patients developed brain metastases during the course of their disease). RNA sequencing of eighty-six samples from primary lung tumors and paired brain metastases of 43 patients was conducted to analyze the tumor immune microenvironment. Our data revealed that matched brain metastases compared with primary lung tumors exhibited reduced tumor infiltrating lymphocytes (TILs), a higher fraction of neutrophils infiltration, decreased scores of immune-related signatures, and a lower proportion of tumor microenvironment immune type I (high PD-L1/high CD8A) tumors. Additionally, we found a poor correlation of PD-L1 expression between paired brain metastases and primary lung tumors. In addition, gene set enrichment analysis (GSEA) showed that some gene sets associated with the immune response were enriched in the metachronous group, while other gene sets associated with differentiation and metastasis were enriched in the synchronous group in the primary lung tumors. Moreover, the tumor immune microenvironment between paired brain metastases and primary lung tumors displayed more differences in the metachronous group than in the synchronous group. Our work illustrates that brain metastatic tumors are more immunosuppressed than primary lung tumors, which may help guide immunotherapeutic strategies for NSCLC brain metastases.