Prognostic significance of programmed cell death receptor ligand PD-L1 expression in chordoma

Introduction. Chordomas are rare malignant neoplasms that are highly recurrent and with limited treatment options. Invasion of the vital structures of the nervous system complicates their treatment. The search for new methods of drug therapy for chordomas is an urgent problem. The aim of the research was to study PD-L1 expression in tumor cells and tumor infiltrating lymphocytes (TILs) in chordoma samples and its interrelation with tumor characteristics and prognosis. Materials and methods. We analyzed PD-L1 expression in 30 primary chordomas using immunohistochemistry and differences in independent groups using Chi-square and Kruskal–Wallis tests. Survival analysis was performed by constructing Kaplan–Meier survival curves. We compared the significance of differences with the logarithmic rank test. Differences were considered significant at p<0.05. Results. PD-L1 expression was detected in tumor cells in 43% of samples and in TILs in 80%. PD-L1 expres-sion in tumor cells and TILs was not associated with the clinical features of the disease. However, PD-L1 expression in tumor cells in all samples correlates positively with the content of this marker in TILs (r=0.409, p=0.028). Different histological variants of chordomas were shown to differ in the content of PD-L1 in both tumor cells and TILs. PD-L1 expression in tumor cells is not a predictor of the disease, while its expression in TILs tends to be a marker of a favorable prognosis (HR=0.1429; p=0.0570). Conclusion. We found the lowest level of PD-L1 expression in both tumor cells and TILs in dedifferentiated chordoma. PD-L1 expression in TILs is associated with a favorable prognosis of chordomas and indicates the potential for the use of checkpoint inhibitors in therapy. Keywords: chordoma, PD-L1, lymphocytes, prognosis, survival