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throat cancer
Throat irritation happens for all sorts of reasons, MedusaGrower, from allergies to illnesses to irritants. If you have red lesions, that could be because you have allergies and drainage, or it could be ulcers from the irritation of smoke. It's highly unlikely that the bong hits you've ingested have actually "burned" your throat. It the smoke were that hot, you couldn't take it into your lungs without great harm. I'm sure the irritation and the nasty components of cannabis smoke--and here I mean the stuff other than THC itself, which is a marvelous anti-inflammatory compound on its own--haven't been tremendously beneficial for your throat. A vaporizer will be a better, healthier way to ingest it.
If you read the links Granny provided above pretty carefully, you'll find them reassuring. In the tests we know of so far, and there haven't been very many of them, but still, there seems to be convincing evidence that even the heaviest cannabis use doesn't seem to correllate with an increase in throat or lung cancers. They think this is because of the marvelous protective effects of THC and probably CBD, too.
Talk to a doctor about your throat irritation if it worries you and have it biposied. If you ask an internist or an ear-nose-throat doctor what the real hallmark signs of impending oral cancers are, they'll usually tell you that chronic irritation and ulcerations, and here I mean irritation that has been there for a period of years, ultimately gives rise into patches of leukoplakia, which are slightly hardened, raised, white areas on the tongue and mucous membrane-covered parts of the mouth. Leukoplakia happens a lot to people who smoke pipes and to people who chew tobacco or dip snuff, and it also happens to cigarette and cannabis smokers but is more prevalent in cannabis smokers who also smoke cigarettes. That doesn't mean it can't happen in people who are cannabis smokers alone, but it probably means the THC is working its protective magic on oral tissues, as they've seen in the studies that have been done on lung and head/neck cancers.