Association of Pack-Years of Cigarette Smoking With Survival and Tumor Progression Among Patients Treated With Chemoradiation for Head and Neck Cancer.

Importance: After 10 pack-years of smoking was initially established as a threshold for risk stratification, subsequent clinical trials incorporated it to identify candidates for treatment deintensification. However, several recent studies were unable to validate this threshold externally, and the threshold for smoking exposure remains unclear. Objective: To estimate the threshold of pack-years of smoking associated with survival and tumor recurrence among patients with head and neck cancer. Design, Setting, and Participants: This single-institution, cohort study included patients with nonmetastatic head and neck cancer receiving chemoradiation from January 2005 to April 2021. Data were analyzed from January to April 2022. Exposures: Heavy vs light smoking using 22 pack-years as a threshold based on maximizing log-rank test statistic. Main Outcomes and Measures: Overall survival (OS), progression-free survival (PFS), locoregional failure (LRF), and distant failure (DF). Results: A total of 518 patients (427 male [82.4%]; median [IQR] age, 61 [55-66] years) were included. Median (IQR) follow-up was 44.1 (22.3-72.8) months. A nonlinear Cox regression model using restricted cubic splines showed continuous worsening of OS and PFS outcomes as pack-years of smoking increased. The threshold of pack-years to estimate OS and PFS was 22. Cox multivariable analysis (MVA) showed that more than 22 pack-years was associated with worse OS (adjusted hazard ratio [aHR] 1.57; 95% CI, 1.11-2.22; P = .01) and PFS (aHR, 1.38; 95% CI, 1.00-1.89; P = .048). On Fine-Gray MVA, heavy smokers were associated with DF (aHR, 1.71; 95% CI, 1.02-2.88; P = .04), but not LRF (aHR, 1.07; 95% CI, 0.61-1.87; P = .82). When 10 pack-years of smoking were used as a threshold, there was no association for OS (aHR, 1.23; 95% CI, 0.83-1.81; P = .30), PFS (aHR, 1.11; 95% CI, 0.78-1.57; P = .56), LRF (aHR, 1.19; 95% CI, 0.64-2.21; P = .58), and DF (aHR, 1.45; 95% CI, 0.82-2.56; P = .20). Current smoking was associated with worse OS and PFS only among human papillomavirus (HPV)-positive tumors (OS: aHR, 2.81; 95% CI, 1.26-6.29; P = .01; PFS: aHR, 2.51; 95% CI, 1.22-5.14; P = .01). Conclusions and Relevance: In this cohort study of patients treated with definitive chemoradiation, 22 pack-years of smoking was associated with survival and distant metastasis outcomes. Current smoking status was associated with adverse outcomes only among patients with HPV-associated head and neck cancer.