There also could be a coinfection, bacterial, fungal or viral, that can cause pain, ulceration, making eating and swallowing difficult, and needs to be treated with the appropriate meds for each. HBO may be controversial in this regard, during treatment, and have not heard of anyone having it, except for some trial, maybe, for increased oxygenation pre, and duringtreatment to the tumor to prevent tumor hypoxia since cancer thrives in low oxygen, which showed was not that effective, and other meds were used instead. HBO is only at certain institutions, takes 1-2 hrs daily treatment.