How would you treat an excised T1N0M0 anal canal well-differentiated squamous cell carcinoma with positive microscopic margin?

As you said, the data is very limited for this set of patients.

The data from the 1980s indicates that even T1N0M0 patients fare poorly with surgery alone (Greenall, Hardcastle) with local control and survival rates being far below what is seen with modern series treated with chemoRT, and thus is not recommended - even with good margins. This being the case, patients treated in this manner likely require RT for optimal outcomes.

Whether or not chemotherapy is required is a more controversial quest...

I mostly agree, but if I used an elective nodal field it would be only to the low pelvis and to the groins. I think the patient should be treated. RT and chemo would be best. I agree with lowering the radiation dose if there were any question of tolerance.

I appreciate all your input. Primarily because of the consequences of failure, my plan is to be aggressive with 45 Gy (1.8) to the primary site, 36 Gy (1.8) to inguinal and lower pelvic nodes, and 32 Gy (1.6) to the upper pelvic nodes with concurrent capecitabine and mitomycin. That being said, I really wonder if the chemotherapy is necessary. Over the years I've had multiple anal cancer patients hospitalized and a few almost die related to toxicity with concurrent 5FU/mitomycin. I've also treat...