GCT-51. IMMUNE CHECKPOINT MOLECULES AND TUMOR INFILTRATING LEUKOCYTES IN THE TUMOR MICROENVIRONMENT ARE ASSOCIATED WITH THE GROWTH OF INTRACRANIAL GERMINOMAS

The role of immune checkpoint molecules and the tumor immune microenvironment in the development of intracranial germ cell tumors remains unclear. In the present study, we investigated the expression of immune checkpoint molecules, as well as the number of tumor-infiltrating lymphocytes (TILs), in intracranial germinomas to determine whether there were any correlations between the statuses of these immune-related molecules/cells and clinical manifestations in patients with germinoma. The 8 patients were categorized based on the duration between symptom onset and pathological diagnosis into the long-term onset (LTO) group (> 1 year of symptoms, 3 patients) and the short-term onset (STO) group (< 1 year of symptoms, 5 patients). Compared with STO tumors, LTO tumors were significantly associated with a lower ratio of programed cell death ligand-1 (PD-L1)–positive tumor cells (p = 0.012), higher number of infiltrating CD3- and CD8-positive lymphocytes (p = 0.016, 0.003, respectively), and lower ratio of programed cell death-1 (PD-1)–positive cells per CD8–positive lymphocytes (p = 0.047). LTO germinomas were significantly smaller in size than STO tumors and tended to be present in patients with atypical tumor location. Our data suggest that the tumor immune microenvironment, including PD-1/PD-L1 signaling, is associated with the growth of intracranial germinomas. Immune checkpoint inhibitors might be a reasonable treatment option for recurrent germinomas or as replacement for radiotherapy in patients with intracranial germinomas.