Complex sentence: It has been used to reduce colon and rectal polyps in people with familial adenomatous polyposis, but it is not known if it decreases rates of cancer, so it is not a good choice for this reason.
Split into simpler sentences: It has been used to reduce colon and rectal polyps in people with familial adenomatous polyposis but it is not known if it decreases rates of cancer. Therefore it is not a good choice for this reason.