Betel‐Quid Exposure and Site‐Specific Prognostic Patterns in Oral Cavity Squamous Cell Carcinoma

OBJECTIVE: Betel-quid chewing is a risk factor for oral cavity squamous cell carcinoma (OCSCC), but its associations with tumour subsite and depth-of-invasion (DOI) related prognosis remain unclear. We examined site-specific associations and exposure-stratified DOI thresholds for disease-specific survival (DSS). METHODS: This retrospective cohort included 454 patients from southern Thailand. Tumour-subsite associations were assessed using multivariable logistic regression. Exploratory DSS thresholds were derived among surgically treated patients using maximally selected log-rank statistics and evaluated with an exposure-stratified Cox model. RESULTS: Of 454 patients, 154 (33.9%) were betel chewers. Exposure was associated with tumours of the buccal mucosa (adjusted odds ratio, 5.43), lip (3.96), retromolar trigone (3.28) and gingiva (3.13), relative to oral tongue tumours. Exploratory DOI thresholds were 7 mm in chewers (log-rank p = 0.006) and 15 mm in non-chewers (p < 0.001). After adjustment, DOI > 7 mm remained associated with poorer DSS in chewers (hazard ratio, 3.55; 95% confidence interval, 1.32-9.52; p = 0.012), whereas the association for DOI > 15 mm in non-chewers was attenuated (hazard ratio, 1.56; 95% confidence interval, 0.97-2.53; p = 0.069). CONCLUSIONS: Betel-quid exposure was associated with OCSCC at quid-contact subsites. Chewers showed a lower exploratory DOI threshold for DSS than non-chewers.