What is the best way to proceed in anal cancer surveillance if PET avidity of the primary is reduced, but still avid at time point <6 months s/p chemo-RT?

I would do serial physical exams every month or two and trust that more than PET-CT.

If it continues to regress, then continue to follow.

If after 6 months it has stopped regressing and you can feel something, can biopsy.