hello,
I second Scott's advice. more frequent surveilence by way of pouchoscopies should be what you need to discuss with a good/caring gastroenteroligist versed in j-pouches.
I've not heard of taking anything as a chemo preventive thats more for if you have active cancer and need chemotherapy.
I have fap (Google if you want to know about the disease) and im not on any preventive meds, i get scopes each 6-8 months and ive been fine (knocking on wood) and my j-pouch is 20 years old. Was operated Oct. 15th 2001.
best wishes & good luck
-len