Hyperbaric oxygen therapy (HBO) is used to treat some complications of head and neck carcinoma treatment. Several patients treated with HBO have had rapid growth of a clinically cured squamous cell carcinoma. Prior studies have produced conflicting evidence about the effect of HBO on tumor growth. This study was undertaken to determine the effects of HBO on established squamous cell carcinoma. Forty Golden Syrian hamster cheek-pouch carcinomas were induced with the established chemical carcinogen 9,10-dimethyl-1,2-benzanthracene. Twenty hamsters underwent 30 HBO dives for 60 minutes each to 2.81 atm, while 20 served as controls. At necropsy, animals receiving HBO therapy had significantly smaller tumors (P < .05) and showed a trend toward fewer cervical metastases (P < .06). HBO therapy with coexistent carcinoma inhibited the established tumor's growth. McDonald, Bradfield, Kinsella, Kumar, Mader, Hokanson, Calhoun, , (1996). Effect of hyperbaric oxygenation on existing oral mucosal carcinoma. The Laryngoscope, 1996 Aug;106(8):957-9. https://www.ncbi.nlm.nih.gov/pubmed/8699908