Prognostic and clinical heterogeneity of PD1 and PD-L1- immunohistochemical scores in endometrial cancers

Introduction: PD1/PD-L1 inhibition (ICi) has recently become a new standard of care for patients with advanced MMR-deficient (MMRd) endometrial cancers. Nevertheless, response to immunotherapy is more complex than the presence of a single biomarker and therefore it remains challenging to predict patients response to ICi beyond MMRd tumors. Elevated PD-L1 expression (CPS ≥ 1) is often used as a prognostic marker as well as a predictive biomarker of response to ICi in different tumor types. In a retrospective, patient derived study, we analyzed PD1- and PD-L1 staining and correlated the results of different scores to clinical data to evaluate the prognostic impact of these scores. Materials and methods: Immunohistochemical analysis of the receptor PD1 and the receptor ligand PD-L1 were performed on TMAs of primary paraffin‑embedded tumor samples. All patients were treated for primary endometrial cancer in the Department of Gynecology and Obstetrics, University Medical Center Schleswig–Holstein, Campus-Lübeck, Germany between the years 2006–2018. The evaluation and determination of the tumor proportion scoring (TPS), the combined positive score (CPS) and the immune cell scoring (IC) was automatically assessed semi-quantitatively, and results were correlated with clinicopathological characteristics and survival. Results: 130 samples were evaluable and 64% showed a positivity (IC > 0) for the receptor PD1 and 56% for the receptor ligand PD-L1. Patients with a PD1 IC Score ≥ 1 showed a significant longer disease-free survival of 140 months (95% confidence interval (CI): 124–158) compared to patients with a lower IC < 1 for PD1 of 89 months (95% confidence interval (CI): 69–110); p = 0.017). Furthermore, the disease-free survival for patients with a CPS ≥ 5 for PD1 was longer (153.7 months (95% confidence interval (CI): 134–173.6) vs. 98.6 months (95% confidence interval (CI): 83–114); p = 0.036). Additionally, a PD1 CPS ≥ 5 showed a better overall survival but the result was not statistically significant. No difference in survival was found between patients with PD-L1 higher or lower than CPS 5. Conclusion: In this study we pointed out that there are significant clinical differences among several immunohistochemical scoring systems. In our trial, a PD1-positivity with CPS ≥ 5 and IC ≥ 1 were significantly associated to a better disease-free survival while there was no association with TPS. The PD1-IC scoring was associated with MMRd while the TPS scoring was not. Therefore, PD1-IC could be more appropriate for endometrial carcinomas compared to TPS and could also add prognostic information beside the more established PD-L1-staining. Further prospective studies are needed for a validation of these scores in combination with other biomarkers.