P14.47 Tissue immune markers for central nervous system germinoma

Abstract

Abstract BACKGROUND Germinoma is the commonest CNS germ cell tumor. An important histological feature is prominent immune cell infiltrates. The composition of such immune cell infiltrates remains under-investigated in the literature. MATERIAL AND METHODS We collected a cohort of 40 cases of intra-cranial germinomas and examined the clinical and histopathological features. The tumor infiltrating immune cells were characterized by immunohistochemistry and image analysis. RESULTS Across the cohort, the mean positivity ± SE of CD3-positive T cell and CD20-positive B cells was 31.2% ± 3.1% and 15.2% ± 2.2%, respectively (p<0.001). The mean positivity of CD4-positive T helper cell and CD8-positive cytotoxic T cell was 19% ± 2.3% and 14.3% ± 1.7%, respectively (p<0.001). PD-L1 expression was detected in 50% of the cases and was observed exclusively in immune cells but not in neoplastic cells. Germinomas with positive PD-L1 expression had significantly more abundant CD3-positive T cells (p=0.001), CD4-positive T helper cells (p<0.001) and CD8-positive cytotoxic T cells (p=0.004) as compared with those lacking PD-L1 expression. Immunostain for HLA-A and HLA-B revealed loss of HLA class I expression occurring in 92.5% of the germinomas. Loss of HLA class I expression was associated with less abundant CD3-positive T cells (p=0.04). CONCLUSION Taken together, the predominant T cells infiltrate and PD-L1 expression suggest anti-PD-L1 therapeutic agents as potential novel treatment option for germinoma patients. The loss of HLA class I may represent one of the mechanisms for tumor immune escape in germinoma.