Grammatically, it is correct with 'burned', the past tense. Burnt is the past participle, and doesn't belong here. I can't comment on the meaning, but I doubt if a doctor or pathologist would choose the words used here.

They're both OK grammatically. The past of "burn" can be either irregular (burnt) or regular (burned). Unfortunately, the sentence doesn't make much sense. I suspect that the problem is a mistranslation of the first verb. I'm not an expert in medical English, but I think that 'used up' or 'exhausted' might be the words you're looking for here, not 'burned off'. NB "Burn off" only means "use up" when we are talking about excess fuel or energy that you want or need to GET RID OF by burning them - for example, doing exercise to burn off calories. It doesn't work in other contexts.