What is your recommended management for a pT1N0 perianal moderately differentiated SCC s/p wide local excision with close 1 mm deep margin?

It’s important to examine the patient before proceeding. Anal and peri-anal cancer can be multi-centric. I have had cases with pathology reports like this who had other areas of clearly invasive disease remaining.

Assuming staging studies are negative and the physical examination reveals only a healing scar, then, in general, one can make a case for deferring further treatment and following the patient closely. Anal cancers, if they recur, are most likely to fail locoregionally; a watchful waiting approach is unlikely to first fail with disseminated disease. I have opted for watchful waiting after local excision for well differentiated peri-anal tumors free of lymphovascular invasion.

However, the presence of an extremely close deep margin...