Little is known about any consequences of swallowing tobacco-free betel-quid (TF-BQ) juice/remnants following chewing and its carcinogenic impact on the upper aerodigestive tract (UADT) to gastrointestinal tract (GIT). We investigated the neoplastic impact of TF-BQ on different anatomical locations along UADT and GIT, and differences according to their histological categories. We conducted a multicenter case-control study examining patients with 2,163 pathology-proven UADT and GIT cancers, comparing them with 2,250 control subjects. Generalized additive models, piecewise regression and polytomous logistic models were applied to identify possible dose-dependent structures and cancer risks. Contrary to nonsignificant GIT-adenocarcinoma risk (aOR=0.9), TF-BQ users experienced a 1.7- to 16.2-fold higher risk of UADT-squamous cell carcinomas than nonusers, with the peak risk discovered in oral neoplasms. We separately observed a curvilinear and linear TF-BQ dose-risk relationship in oral/pharyngeal/esophageal and laryngeal cancers. Chewers of betel inflorescence were generally at a greater UADT cancer risk. A higher first-piecewise increased risk of esophageal cancer was recognized among areca-fluid swallowers than among nonswallowers (continuous aOR=1.12 vs. 1.03). TF-BQ use accounted for 66.1-78.7% and 17.8-33.2% of the cases of oral/pharyngeal and esophageal/laryngeal cancers, respectively. However, a reduction from heavy TF-BQ consumption to low-to-moderate consumption only reduced 11.3-34.6% of etiologic fraction of oral/pharyngeal cancers. Alcohol supra-additively modified the risk of TF-BQ in determining the development of oral, pharyngeal and esophageal cancers. In conclusion, the interplay of TF-BQ and alcohol/tobacco use, combined with how chewing habit is practiced, influences carcinogenic consequences on anatomically diverse sites of UADT and GIT cancers, and histologically different types.