Screening for colorectal cancer

Kenneth Marshall's views on screening for colorectal cancer^1,2 are a welcome breath of fresh air in the triumphalist haze propagated by Sidney Winawer and Ann Zauber.³ In the real world, it is extremely important to balance potential benefit with risk. In the case of screening for colorectal cancer the benefits are very small and the risks anything but insignificant. It is astonishing that Winawer and Zauber in their rebuttal state that “medical harms have been studied and have not been demonstrated.”⁴ One of the studies they quote in support of this statement clearly demonstrated a complication rate of 0.5% from colonoscopy; of the patients with complications 85% required surgical intervention.⁵ This is a very serious toll that might be acceptable for patients under investigation for cancer but is unacceptable for the large number of people who have a colonoscopy as a result of a false- negative occult blood screen.

Nobody will argue against Winawer and Zauber's closing statement that “losing even one life prematurely is a tragedy,”⁴ but this argument does not overcome the naïveté of their case in the light of the very small benefit, the substantial harm and the enormous opportunity cost of screening for colorectal cancer.

Signature

Charles J. Wright
Centre for Clinical Epidemiology & Evaluation Vancouver Hospital & Health Sciences Centre Vancouver, BC