When a large malignant appearing GI mass is encountered on endoscopy but biopsies show dysplasia or carcinoma in situ, would you recommend additional biopsies or proceed with treatment for invasive cancer?   

This is an issue that comes up fairly regularly. The simple answer is that we should not treat (with radiation or chemotherapy) without a cancer diagnosis, but life is rarely that simple and every rule has exceptions. Certainly, whenever possible, a repeat biopsy should be done, or, as @Sushil ...

Generally we favor repeat bx but sometimes ask the pathologist to review path with clinical information. This may lead to a change interpretation to possible invasion. Also if imaging shows locally advanced disease then we have proceeded with treatment after discussion with patient. 

These are all good points. I also like to present these cases in conference and reach a multidisciplinary consensus about the risk/benefit ratio and suspicion before treating without confirmed invasive cancer.

Agree with all of the above. It's very unlikely that either a review of the initial pathology or a repeat biopsy will be non-diagnostic, but occasionally our hand is forced. All of this discussion is predicated on the assumption that management of the mass with surgery alone (which wouldn't re...