PD-L1 expression of high grade glial tumors at diagnosis and change of expression status at recurrence.

Abstract

2035 Background: PD-L1 expression status is the main predictive factor for response to immune checkpoint inhibitors. PD-L1 status may change over time with the impact of therapies. The aim of this study is to determine if PD-L1 expression status changes in recurrent gliomas after chemoradiotherapy. Methods: Thirty eight patients with recurrent high grade gliomas who had surgical excision at least two times were included in this retrospective cross-sectional study. Nine patients were excluded because of the lack of appropriate pathology slides for pathologic evaluation. PD-L1 expression of 29 patients was evaluated by an expert pathologist with immunohistochemical methods. PD-L1 positivity was defined as expression in ≥1% of tumor cells. Change in PD-L1 expression status was defined as an absolute 5% difference between two resections. Results: Of the 29 patients, 15 patients (51.7%) had PD-L1 expression in ≥1% of tumor cells and 7 patients (24.1%) had PD-L1 expression in ≥10% of tumor cells. Tumor PD-L1 expression (defined as expression in ≥1% of tumor cells) was positive in 15 (51.7%) of 29 patients at diagnosis and at the time of recurrence. The PD-L1 status did not change in 17 patients (58.6%). 8 patients had PD-L1 negative tumors both at diagnosis and at recurrence, while 9 patients had PD-L1 positive tumors both at diagnosis and at recurrence. In 6 patients (20.7%) a negative-to-positive switch and in 6 patients (20.7%) a positive to negative switch were seen. Tumor PD-L1 expression increased in 7 of 29 patients (24.1%) and decreased in 9 of 29 patients (31.1%). PD-L1 expression remained stable in 13 of 29 patients (34.4%). The change in PD-L1 status over time was not statistically significant. Conclusions: More than 50% of high grade glial tumors express PD-L1 at diagnosis, so these tumors are good candidates for immune checkpoint inhibitors. The expression status changes in more than 40% of high grade glial tumors at recurrence, so immune responsiveness of glial tumors can be modified by treatments like chemotherapy and radiotherapy.