What proportion of gi endoscopy samples get reviewed by peer pathologists? if a sample triggers a pathology panel review, does that mean there is suspicion of malignancy, or is it just a random selection?

It depends. If the pathologist has doubts about what he/she sees, they ask a colleague to review. Some academic centers do it routinely. There is no particular universal rule, It does not have to be cancer to trigger a review.

In can be either or both. If a pathologist has any concern s/he may consult other pathologists. Most pathology department do a second review of about 10% cases on a random basis. Wish you good health!