Revisiting the Role of PD-L1 Overexpression in Prognosis and Clinicopathological Features in Patients with Oral Squamous Cell Carcinoma

Background: PD1 and its ligand PD-L1 are related to prognosis in many solid tumors; however, their role in oral squamous cell carcinoma (OSCC) remains unclear. Methods: A retrospective monocentric study including all patients with OSCC diagnosed and treated between January 2020 and May 2022 was performed. PD-L1 expression was assessed per a combined positive score (CPS), considering a CPS of > or equal to 1 as positive (1–20 indicating “low expression” and ≥20 indicating “high”). A descriptive analysis of the patient cohort and tumors was performed, including tumor size, stage, lymph node involvement, recurrence, and survival. Results: In total, 65 patients (65 tumors) were analyzed. A total of 66.15% of the tumors were in advanced stages (III-IV), of which 97.67% expressed PD-L1+, compared with 71.42% in the early stages (I–II). T4 tumors expressed PD-L1 in 100% of cases, compared with 54% in T1 tumors. A total of 50.79% of the tumors showed lymph node involvement (pN+), with 100% of the pN+ showing PD-L1+. The prevalence of pN+ was 59.38% vs. 40.63% for high vs. low PD-L1 expression, respectively. Patients’ follow-ups ranged from 2 to 34.5 months. No significant difference was seen between overall survival (OS) and PD-L1 +/− (CPS ≥ 1 vs. CPS < 1) or high (CPS ≥ 20) and low (CPS < 20) PD-L1 expression (p < 0.97 and 0.64, respectively). Conclusions: The method used to measure PD-L1 (a laboratory test with Dako 22C3 anti-PD-L1 primary antibodies) was reliable and accurate, with a correlation coefficient between PD-L1 expression in the biopsy and the surgical piece of 0.83 (p < 0.0001). A CPS of ≥1 was observed in large tumors (p < 0.001) and was correlated with that of lymph node metastases (p < 0.004). Further analysis of PD-L1 expression in OSCC and studies to determine its relevance in tumor biology and prognosis is needed.