Expression of PD-1 and PD-L1 in Kaposi’s Sarcoma and Their Association with Clinicopathologic Findings: A Retrospective Observational Study

Background Kaposi sarcoma (KS) is a multifocal vascular neoplasm that progresses from patch/plaque to tumor stage. Expression of PD-1 and PD-L1 is a key immune checkpoint feature in skin malignancies, but data on their role in KS are limited. We aimed to evaluate PD-1 and PD-L1 expression in KS and to assess their associations with pathologic stage and clinical features. Methods In this retrospective observational study, 46 patients with KS referred to Razi Hospital in Tehran were included. PD-1 and PD-L1 expression was evaluated by immunohistochemistry in tumor tissue and adjacent non-tumor tissue. Associations between marker expression, pathological stage, HIV status, and clinical relapse were analyzed. Results Intratumoral PD-L1 expression in tumor-stage samples was significantly higher than in patch/plaque-stage samples, while intratumoral PD-1 expression was significantly higher in patch/plaque lesions than in tumor-stage lesions. Similar stage-related differences were observed when a 5% cut-off for positivity was applied. In contrast, neither PD-1 nor PD-L1 expression in intratumoral or peritumoral areas showed a significant association with HIV status or clinical relapse. Conclusion Higher PD-L1 expression was associated with more advanced stages of KS, whereas PD-1 and PD-L1 expression was not related to HIV status or relapse. The upregulation of PD-1/PD-L1 expression suggests that anti-PD-1/PD-L1 immunotherapy may be a potential option for advanced KS.