Abstract
OBJECTIVE: Head and neck (HN) cancer comprises the neoplasms originating from the oral cavity, pharynx and larynx. We aimed at reviewing the available literature on the effect of smoking cessation on HN cancer risk. METHOD: We conducted a systematic search in Medline, PubMed and Embase to June 2022. We abstracted or calculated relative risks (RR) and 95% CIs of HN cancer after cessation of tobacco smoking (both former smoking status and duration of quitting) and combined them using random effects meta-analyses. Papers included were case-control or cohort studies available in the English language. Studies investigating smoking cessation after cancer diagnosis, case reports, intervention studies or animal studies were excluded. Quality and susceptibility to bias of each included study were evaluated using the Newcastle-Ottawa Scale. Publication bias was assessed using funnel plot and Egger's test. RESULTS: A total of 65 studies were included in the review, including 5 cohort and 60 case-control studies. The RR of HN cancer for former smokers compared with current smokers was 0.40 (95% CI 0.35 to 0.46). In an analysis by cancer site, the RR of oral cancer was 0.44 (95% CI 0.35 to 0.55), that of pharyngeal cancer 0.44 (95% CI 0.32 to 0.60) and that of laryngeal cancer 0.38 (95% CI 0.29 to 0.50). The dose-response meta-analysis was based on 37 studies. The RR per 10-year increase in smoking cessation was 0.47 (95% CI 0.43 to 0.52). CONCLUSIONS: The risk of HN cancer declines within the first 5 years of quitting smoking. Quitting smoking is an essential element of HN cancer prevention. TRIAL REGISTRATION NUMBER: The protocol has been deposited in the PROSPERO repository (CRD42022338262).