OSCC has been known for a long time, and its behavior in many ways is well understood and predictable. That statement is not an absolute, as all the people on this board will testify to, as there are individual idiosyncrasies too numerous to mention.

So, we can predict that even with clear margins, the likelihood that there are some micro metastasis, that are too small to even show up on any type of scans, into the surrounding tissues is something we should treat for even though we can't see them. Ask how many people with surgical only solutions have recurrences (the wrong word.... I think I will gain the wrath of most otolaryngologists when I use the phrase "incomplete primary treatment", which attorneys like to use a lot) in about 18-24 months after they were told that the doctor "got it all". The answer to that question is too many, by the way.

We also understand its known pathways of metastasis, how it usually (nothing is 100%) wants to go south into the lymph system and the cervical nodes found in the neck, and if not caught there into the chest and the vital organs where the consequences become increasingly dire. The chemo is a radio sensitizer to make radiation work better...think belt and suspenders.

Doctors decisions can be highly conservative, or unspeakably cavalier and disregarding of clinical experience in the big institutions. So be thankful that the team he is seeing is the former not the latter.

PET scan immediately after any treatments are notoriously full of false positives as they are not a test for cancer, but sugar uptake which is also a by-product of the healing process. MRI's and CT's do not have this issue but look for soft or hard tissue abnormalities.

Lastly re the tobacco. When this is the etiology, there is an issue of field carcinogenesis, which I have explained on these boards a few hundred times, so please take a run through the search engine. Short answer is that he has contaminated a large area that is more than his mouth with his habits/life style, and the cancers associated with each anatomical site occur at different times.