This is Episode thirteen: Oral Cavity Three — PORT versus Post-op Chemo-RT: The "Big Two."In the last two episodes, we established that oral cavity cancer is a surgical disease and that the clinically node-negative neck requires elective treatment when depth of invasion exceeds three to four millimeters. Now the surgery is done. The pathology report is in your hands. The question becomes: what adjuvant therapy does this patient need?This is the domain of two landmark trials that every radiation oncologist must know cold: R-TOG ninety-five-oh-one by Cooper and E-O-R-T-C twenty-two-nine-three-one by Bernier—both published in the New England Journal of Medicine in 2004. These trials established the "Big Two" indications for concurrent chemoradiation: positive margins and extranodal extension.After this episode, you should be able to answer in one sentence: PORT versus chemo-RT, and why?This episode covers the evidence for post-operative radiation, when to add chemotherapy, the critical importance of timing, and how to apply these principles to real cases. Let's get into it.