Hmm, I'm not a reimbursement expert by any means, but when one of my providers does a colonoscopy, they don't wait to find out if a colon polyp is malignant before they excise it and bill out a claim. Of course they'll note the results in the patient chart, but they won't necessarily wait for a super-specific diagnosis before submitting a claim.
e.g, A patient could have C18.2 or D12.2. Only one of those is cancerous. But since the operative physician doesn't know which it is until pathology gets their hands on it, there are codes like K63.5 for "polyp of colon" or D48.9 "neoplasm of uncertain behavior" which are specific and billable, but don't make a determination of what exactly the patient has. It's a way of half-diagnosing the problem, since it involves a second physician for the confirmation.
As to the actual dollar amounts for services, that would probably depend on what specific service is being performed. I know colonoscopies pay differently if they're screenings vs operative, but I couldn't tell you how much (god bless payment posters, who keep coders from having to do this). However, the type of service performed is determined at the date of service, not by any diagnosis. You don't get paid differently for an operative colonoscopy for cancer than you do for an operative colonoscopy for benign polyps, so long as the same amount of work was done. At least you shouldn't. The same service was performed, just for two different reasons.
Hope this helps.