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Intracranial solitary fibrous tumor (SFT) /hemangiopericytoma (HPC) are rare, however, these tumors are often associated with aggressive clinical course with recurrence and/or extracranial metastasis. PD-1, PD-L1 play important roles as immune-checkpoint mediators within tumor microenvironment, and the antibodies to these molecules are now approved for the treatment of various kinds of cancers. Some mechanisms of activation of PD-L1 are reported, including cytokines or chemokines from immune cells in tumor microenvironment, and genetic mutations such as translocation, or amplification. We have investigated the expression of PD-1, PD-L1, and tumor infiltrating lymphocytes (TIL) in 16 cases of SFT/HPC by immunohistochemistry. Kaplan-Meier method and log-rank/Wilcoxon tests were used to analyze the relationship between their expression with overall survival (OS), progression free survival (PFS), metastasis free survival (MFS), and time to treatment failure (TTF; metastasis or death). Additionally, we have analyzed amplification of PD-L1 gene by FISH, translocation between promotor region of CIITA and PD-L1 by PCR, and mutation in 3’-UTR by immunohistochemistry with antibody recognizes C-terminus (clone; SP-142) of PD-L1. PD-L1 was expressed in most of tumor cells. The intensity of PD-L1 expression was negatively associated with MFS (p=0.04), and diffuse pattern of PD-L1 expression showed trends towards shorter TTF compared with partial expression (p=0.08). Notably, with the combination analysis of PD-L1 and CD8(+) TIL, the diffuse PD-L1 expression with less CD8(+) was significantly associated with shorter TTF (p=0.005). However, there was no significant relevance between the expression of those immune-checkpoint molecules and OS or PFS. Although neither amplification of PD-L1 gene, 9p24.1, nor translocation between CITTA and PD-L1 were observed, difference in immunohistochemistry with two different anti-bodies was observed. In intracranial SFTs/HPCs, tumor immunity mechanism associated with PD-1/PD-L1 may play an important role in their extracranial metastases, and mutation in 3’-UTR may be a cause of PD-L1 activation in SFT/HPC.

RARE-34. TUMOR IMMUNITY AND EXTRACRANIAL METASTASES, AND MECHANISM OF PD-L1 EXPRESSION IN INTRACRANIAL SOLITARY FIBROUS TUMOR/HEMANGIOPERICYTOMA