In my wifes case, it is tongue cancer so it could be different with "retromolar trigone region". I wasn't able to find the information in my notes but using the link provided by Leslie, I think what we were told any of of the following and they would recommend chemo/radiation:
1. Margins that were not clear
2. Cancerous lymph nodes (I think they may have said on both sides)
3. Extracapsular spread (my understanding of this was whether they felt the cancer was contained within the lymph nodes)
4. Perineural invasion (my understanding the cancer growing around a nerve)
5. Vascular embolism (not sure on this but would believe cancer growing close or around artery)
That is the best that I can make out of it, if you use either of the links from Leslie and are able to read the flow charts, you should be able to determine the rationale that they used. For this information, I used page 24, Cancer of the Oral Cavity. Again in my wife's case, she struck out on the first 2 items above so will be starting chemo and radiation next Monday.

Colleen, they may have talked about well or poorly differentiated cells in the tumor but I don't recall. I know my wife's tumor was not as large as many on this site, I believe hers was 2.5cm long and 1cm thick, so may not have been an issue.

Karen, wishing you and Chip a long healthy future.