Immunohistochemistry-based hypoxia-immune prognostic classifier for head-and-neck cancer patients undergoing chemoradiation – Post-hoc analysis from a prospective imaging trial

•Low CAIX and high TIL levels independently result in superior locoregional control.•The CAIX-TIL classifier exhibits a superior predictive power than each marker alone.•The classifier stratifies between three distinct prognostic groups.•Baseline CAIX levels correlate with [18F]FMISO SUV in week 2 of chemoradiation. As both tumor hypoxia and an immunosuppressing tumor microenvironment hamper the anti-tumor activity of radiotherapy in head-and-neck squamous cell carcinoma (HNSCC), we aimed to develop an immunohistochemistry-based hypoxia-immune classifier. 39 patients receiving definitive chemoradiation for HNSCC within a prospective trial were included in this analysis. Baseline tumor samples were analyzed for the hypoxia marker carbonic anhydrase IX (CAIX) and tumor-infiltrating lymphocytes (TILs) and were correlated with [18F]-misonidazole ([18F]FMISO) PET measurements. The impact of the biomarkers on the locoregional control (LRC) was examined using Cox analyses and concordance index statistics. Low CAIX (HR = 0.352, 95%CI 0.124–1.001, p = 0.050) and high TIL levels (HR = 0.308, 95%CI 0.114–0.828, p = 0.020) were independent parameters for improved LRC and did not correlate with each other (Spearman’s ρ = 0.034, p = 0.846). Harrell’s C was 0.66 for CAIX and TIL levels alone and 0.71 for the combination. 2-year LRC was 73%, 62% and 11% for the prognostically good (CAIXlow/TILhigh), intermediate (CAIXlow/TILlow or CAIXhigh/TILhigh) and poor groups (CAIXhigh/TILlow), respectively (p = 0.001). Focusing on T lymphocytes, the hypoxia-immune classifier could still stratify between favorable (CAIXlow/CD3 + TILhigh), intermediate (CAIXlow/CD3 + TILlow or CAIXhigh/CD3 + TILhigh) and poor subgroups (CAIXhigh/CD3 + TILlow) with a 2-year LRC of 80%, 59% and 14%, respectively (p = 0.001). There was a positive correlation between baseline CAIX levels and [18F]FMISO SUV in week 2 of chemoradiation (ρ = 0.324, p = 0.050), indicating an association between higher baseline CAIX expression and tumor hypoxia persistence. We developed a clinically feasible hypoxia-immune prognostic classifier for HNSCC patients based on pre-treatment immunohistochemistry. However, external validation is required to determine the prognostic value and the potential usage for personalized radiation oncology.