Abstract
BackgroundCigarette smoking is associated with nasopharyngeal cancer (NPC) risk. Whether quitting reduces the risk is unclear. We investigated the associations of NPC with duration of and age at quitting in an endemic region.MethodsWe investigated the associations between NPC and quitting in a multicenter case-control study in Hong Kong with 676 newly diagnosed NPC cases and 1,285 hospital controls between 2014 and 2017, using a computer-assisted self-administered questionnaire. Multivariable unconditional logistic regression yielded adjusted odds ratios (AORs) of NPC by quitting status, duration and age of quitting, combinations of duration and age of quitting, and quitting to smoking duration ratio, compared with current smoking.ResultsQuitting (AOR: 0.72; 95% CI: 0.53–0.98) and never smoking (0.73, 0.56–0.95) were associated with lower NPC risk. NPC risk decreased with (i) longer quitting duration (p < 0.01), reaching significance after 11–20 (0.62, 0.39–0.99) and 21+ years (0.54, 0.31–0.92) of quitting; (ii) younger quitting age (p = 0.01), reaching significance for quitting at <25 years (0.49, 0.24–0.97); and (iii) higher quitting to smoking duration ratio (p < 0.01), reaching significance when the ratio reached 1 (0.60, 0.39–0.93). Quitting younger (age <25) appeared to confer larger reductions (49% for ≤10 years of quitting, 50% for 11+ years) in NPC risk than quitting at older ages (25+) regardless of quitting duration (16% for ≤10 years, 39% for 11+ years).ConclusionsWe have shown longer duration and younger age of quitting were associated with lower NPC risk, with dose-response relations. Our findings support including smoking as a cause of NPC. Stronger tobacco control measures and quitting services are needed to prevent NPC.
Highlights
Despite its similar cellular or tissue lineage, nasopharyngeal carcinoma (NPC) shows a unique epidemiologic pattern among head and neck cancers
No difference was observed for housing type at the age of 10 years, consumption of salted fish at age 6–12, and number of cigarettes smoked per day in ever smokers (Table 1)
The odds ratios (ORs) of NPC generally decreased with increasing duration of quitting (p for trend:
Summary
Despite its similar cellular or tissue lineage, nasopharyngeal carcinoma (NPC) shows a unique epidemiologic pattern among head and neck cancers. In 2004 and 2012, the International Agency for Research on Cancer reported that cigarette smoking increases NPC risk in both endemic and nonendemic regions [10, 11], while the Health Consequences of Smoking Report by the US Surgeon General in 2014 only concluded on the carcinogenicity for oropharynx but not for nasopharynx due to insufficient evidence [12]. Further evidence has emerged [1, 13,14,15,16] and a meta-analysis showed that every 10 more pack-years of smoking was associated with 15% higher risk of NPC [17]. Our recent individual data meta-analysis of cohort studies in endemic regions has provided strong evidence for a causal relation between smoking and NPC [18]. We investigated the associations of NPC with duration of and age at quitting in an endemic region
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