Ultra‐high combined positive score and high serum albumin are favorable prognostic biomarkers for immune checkpoint inhibitors in head and neck squamous cell carcinoma.

Background: Biomarkers that predict response to immune checkpoint inhibitor (ICI) in recurrent metastatic squamous cell carcinoma of the head and neck (RMHNSCC) are not well known. Methods: We prospectively measured the combined positive score (CPS) and administered ICI to patients with RMHNSCC. Results: Of 51 patients, 23 patients had a CPS <20 and 12 patients (23.5%) had a CPS ≥90. CPS showed a negative correlation with serum albumin. Survival analysis showed a 2‐year survival rate of 24.1%. In multivariate analysis, CPS ≥90 (HR 0.3026, p = 0.02614) and albumin >3.5 (HR 0.3463, p = 0.01354) were the significant factors and plus chemotherapy (HR 0.4648, p = 0.07632) was not significant. Seven patients (14%) with CPS ≥90 and albumin >3.5 showed a 2‐year survival rate of 66. 7%. Conclusions: CPS ≥90 and albumin >3.5 cases are a subgroup of RMHNSCC that respond extremely well to ICI. [ABSTRACT FROM AUTHOR]