In the article I linked above it was noted that most of the cancers that occur in the j-pouch occur in the ATZ (anal transition zone). This is the area between the rectal cuff and the anus. The pouch attachment suture line would be between the rectal cuff and the j-pouch.
Overall, the incidence is very low and is mostly in patients with precolectomy cancer or dysplasia. So it is important to have perspective and not get alarmed that there may be some risk. Remember, having a pouchoscopy does not prevent or cure cancer. It just increases the likelihood of detecting it.