However, cancers also occur in areas of the colon too far from the anus to be accessible to sigmoidoscopes.
Colonoscopy uses an instrument capable of examining the whole colon.
Need for colonoscopy is controversial, and the procedure is not a routine study since it requires anesthesia, is more time-consuming, and more expensive to carry out. There is also a small risk of perforating the colon. An international research team from Canada, Germany and the UK examining the incidence of various gastrointestinal cancers among 73,076 men and women who had received heart or kidney transplants, found that there was a nearly three-fold reduction in the incidence of rectal cancer among them. The effect was greater in men than in women, and also was more pronounced among heart transplant cases. All transplant patients receive continuous immune-suppressing therapy to prevent organ rejection.