Would you treat the inguinal nodes in a patient who had an adenocarcinoma excised from the anal canal?  

I would definitely include the external iliac nodes for such a case. I would also definitely add the inguinal nodes if the cancer were extending to the verge or beyond.  I would also scrutinize the imaging studies very carefully; a 1-2 cm inguinal node has to be of greater concern in this setti...

I have had patients with very low rectal cancer (4 cm from the verge) recur in the inguinal nodes after definitive radiation.  For a clearly involved anal canal, I would always treat.