Objectives/Hypothesis: The tumor immune microenvironment in temporal bone squamous cell carcinoma (TBSCC), including the programmed death-ligand 1 (PD-L1) expression and tumor-infiltrating lymphocytes (TILs), has not been established. Study Design: Retrospective cohort study. Methods: We performed immunohistochemistry analyses to retrospectively analyze 123 TBSCC cases for PD-L1 expression and TILs and their prognostic significance. We also evaluated the prognostic correlations between these immunomarkers and the therapeutic responses to chemoradiotherapy (CRT). Results: PD-L1 expression (≥1%) was detected in 62 (50.4%) TBSCC cases and was significantly associated with worse prognosis: progression-free survival (PFS), P <.0001; overall survival (OS), P =.0009. A high density of CD8+ TILs was significantly associated with better prognosis (PFS, P =.0012; OS, P =.0120). In contrast, a high density of Foxp3+ TILs tended to be associated with an unfavorable prognosis (PFS, P =.0148; OS, P =.0850). With regard to the tumor microenvironment subtypes defined by CD8+ TILs and PD-L1 expression, the CD8low/PD-L1+ group showed significantly worse prognosis. Among the 36 neoadjuvant CRT-treated cases, PD-L1 expression was significantly associated with worse OS (P =.0132). Among the 32 CRT-treated cases without surgery, a high density of CD8+ TILs tended to be more highly associated with complete response to CRT compared to a low density of CD8+ TILs (P =.0702). Conclusions: These results indicate that the evaluation of the tumor immune microenvironment may contribute to the prediction of prognoses and the selection of an individualized therapeutic strategy for patients with TBSCC. Level of Evidence: 4 Laryngoscope, 131:2674–2683, 2021.
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