The analysis of subsets of tumor infiltrating lymphocytes (TILs) representing main types of cells such as CD3+, CD8+, CD45RO+, FOXP3+ and PD-1+, and the expression of PD-L1 in SCLC brain metastases and four matched primary tumor specimens using immunohistochemistry showed the active immune microenvironment in SCLC brain metastases. This evidence concerns the gene CD8A and small cell lung carcinoma.