I think it would be a really good idea to get a 2nd opinion from another qualified GI. I agree that 5-ASA discourages cancer and ask your new doctor if he agrees that CRC is a slow developing cancer.
Is there that much of an increase of colorectal cancer with no clinical inflammation?
We aren't doctors and therefore not qualified to 2nd guess your GI. That's why getting another doctor's opinion is so important. After all who knows if your original doc's recommendation is based on medical best practices or because he needs to pay his grandchildren's college education. lol