Programmed Death-Ligand 1 Expression, Microsatellite Instability, Epstein–Barr Virus, and Human Papillomavirus in Nasopharyngeal Carcinomas of Patients from the Philippines

Most nasopharyngeal carcinomas (NPCs) in a high-incidence population are driven by Epstein–Barr virus (EBV) infection. EBV-associated malignancies have increased expression of the programmed death-ligand 1 (PD-L1). Immunotherapy agents targeting the PD-1/PD-L1 pathway have achieved durable treatment effects in patients with various cancer types including EBV-associated malignancies. In this study, we sought to investigate PD-L1 expression in a cohort of patients with NPCs from the Philippines. Fifty-six NPCs were studied for PD-L1, p16, and DNA mismatch repair (MMR) deficiency by immunohistochemistry. One case with MMR deficiency was also assessed for microsatellite instability (MSI) by polymerase chain reaction. EBV and human papillomavirus (HPV) status were tested by in situ hybridization. All NPCs were p16 negative. Three of the 56 NPCs (5%) were EBV negative (EBV−) and HPV negative, while one NPC (1/56, 2%) was EBV positive and showed MSI (EBV+/MSI). Positive PD-L1 expression (PD-L1+), defined as membranous staining in ≥1% tumor cells, was seen in 64% (36/56) of NPCs. All three EBV− NPCs were PD-L1+ as was the EBV+/MSI NPC. PD-L1+ was seen significantly more often in NPCs from non-smokers than those from smokers (23/28, 82% vs 9/18, 50%; P = 0.047). PD-L1+ was not associated with pT, pN, distant metastasis, or clinical stage (P > 0.05). PD-L1+ was not associated with overall survival (P = 0.473). In summary, our results show frequent PD-L1 expression in NPCs regardless of EBV status and a preferential PD-L1 expression in non-smokers. MSI and HPV positivity are exceedingly rare in NPCs.