Tumor Histological Grade and Immunotherapy Response in Patients With Recurrent or Metastatic Head and Neck Squamous Cell Carcinoma

Importance: Tumor histological factors that predict immunotherapy response in patients with recurrent or metastatic head and neck squamous cell carcinoma (HNSCC) are not well defined. Objective: To investigate the association between tumor grade and immunotherapy response in patients with recurrent or metastatic mucosal HNSCC. Design, Setting, and Participants: In this retrospective cohort study, the medical records of 60 patients with recurrent or metastatic mucosal HNSCC treated with immune checkpoint inhibitors at Johns Hopkins Hospital between July 1, 2015, and January 22, 2020, were reviewed. Exposures: High-grade tumors (HGTs) vs low-grade tumors (LGTs) in recurrent or metastatic HNSCC. Main Outcomes and Measures: Patients were divided into 2 groups: those with LGTs (well differentiated and moderately differentiated) and those with HGTs (poorly differentiated). The main outcome was a clinically beneficial immunotherapy response, defined as complete response or partial response. Univariable and multivariable logistic regressions were conducted to calculate odds ratios for each variable's association with immunotherapy response. Survival differences were evaluated using Kaplan-Meier survival curves with multivariable Cox proportional hazards regression models. Results: The 60 patients (35 with HGTs and 25 with LGTs) had a mean (SD) age of 64.6 (8.88) years; 51 were male (85%); and 38 were current or former smokers (63%). The oropharynx was the most common primary tumor site both in patients with HGTs (22 of 35; 63%) and those with LGTs (12 of 25; 48%). Bivariate analysis showed the proportion of patients having a beneficial response to immunotherapy was greater for patients with HGTs (12 of 35; 34.3%) than those with LGTs (2 of 25, 8.0%) (difference, 26.3%; 95% CI, 7.3%-45.3%). Upon multivariable analysis, patients with HGTs had 5.35-fold increased odds (95% CI, 1.04-27.37) of having a clinically beneficial response to immunotherapy. Among patients with available tumor genomic profiling data, the mean tumor mutational burden was greater for patients with HGTs (mean [SD], 8.6 [5.4] mut/Mb; n = 8) than patients with LGTs (mean [SD], 3.6 [1.1] mut/Mb; n = 4) (difference = 5.0 mut/Mb; 95% CI -1.4 to 11.4 mut/Mb; Cohen d = 1.2). Conclusions and Relevance: In this cohort study, tumor grade was independently associated with immunotherapy response in patients with recurrent or metastatic mucosal HNSCC. These findings highlight the potential role of tumor grade in predicting immunotherapy response in mucosal HNSCC..