Development of a Hypoxia-Immune Prognostic Classifier for Head-and-Neck Cancer Patients Undergoing Radiotherapy ― Results From a Prospective Imaging Trial

Abstract

Tumor-infiltrating lymphocytes (TILs) correlate with an improved outcome of head-and-neck squamous cell cancer (HNSCC) patients undergoing radiotherapy and are influenced by the tumor microenvironment and tumor-associated hypoxia. The present analysis is based on a prospective imaging trial and analyzes the value of TILs and tumor-associated hypoxia to stratify HNSCC patients according to their response to radiotherapy.A total of 49 patients with locoregionally advanced HNSCCs were prospectively enrolled in this trial and underwent longitudinal hypoxia PET imaging using fluoro-18 misonidazole ([18F]FMISO) in weeks 0, 2 and 5 during chemoradiation. Tumor hypoxia was assumed for a tumor-to-background SUV (contralateral sternocleidomastoid muscle) exceeding 1.4, and an early hypoxia response was defined as a decrease in the normalized maximum intratumoral SUV (FMISO-SUVindex) between weeks 0 and 2. Pre-treatment tumor biopsies were analyzed for TILs and the hypoxia tissue marker carbonic anhydrase IX (CAIX). Trial patients were stratified into 4 subgroups based on their TIL numbers (> 100 vs. < 100 TILs/HPF) and expression of CAIX (above vs. below median H-score), and locoregional control (LRC) and progression-free survival (PFS) rates for all subgroups were assessed using Cox and subsequent concordance analyses (Harrell's C).High TIL levels correlated with improved LRC (HR = 0.279, P = 0.011) and PFS (HR = 0.276, P = 0.006). Similarly, a decrease in the FMISO-SUVindex within the first 2 weeks of treatment corresponded with better LRC (HR = 0.321, P = 0.015) and PFS (HR = 0.402, P = 0.043). Harrell's C was 0.68, when TILs and early hypoxia PET response were combined. The hypoxia PET-based hypoxia-immune classifier separated 3 distinct prognostic patient subgroups, a favorable (TILhigh/ early PET response), and intermediate (TILhigh/no early PET response or TILlow/early PET response) and a poor (TILlow/no early PET response) prognostic group with 2-year LRC of 71%, 33% and 0%, respectively. Low pre-treatment tissue levels of CAIX were also prognostic for improved LRC (HR = 0.352, P = 0.050) but not PFS (HR = 0,468, P = 0,087). Harrell's C was 0.66 for CAIX and TILs separately and 0.71 for the combination. The immunohistochemistry-based immune-hypoxia classifier similarly stratified between a favorable (CAIXlow/TILhigh), an intermediate (CAIXlow/TILlow or CAIXhigh/TILhigh) and a poor (CAIXhigh/TILlow) subgroup with 2-year LRC rates of 73%, 62% and 11%, respectively.We developed a hypoxia PET-based hypoxia-immune classifier that was able to separate HNSCC patients into 3 distinct prognostic subgroups based on their tumor biology. These subgroups could also be stratified in a clinically feasible, immunohistochemistry-based classifier with comparable model accuracy. Therefore, this hypoxia-immune classifier could help to stratify prognoses of HNSCC patients undergoing radiotherapy pending validation in an external cohort.