Screening for colorectal cancer

Charles Wright, Brian Budenholzer, Gordon Brock, Vydas Gurekas and Steven Latosinsky state that colorectoral screening is associated with substantial harms and few benefits. They do not support the views of the Ontario Expert Panel on Colorectal Cancer Screening, which, after reviewing all the evidence on benefit and harms, recommended colorectal cancer screening with fecal occult blood testing for average-risk people 50 years old and older.1 The US Preventive Services Task Force, the American Cancer Society, an Australian task force, the European Group for Colorectal Cancer Screening and a consortium of US gastroenterology and surgical societies also recommended screening.2 The evidence included a 33% reduction in mortality for annual fecal occult blood test screening.3 If this reduction in mortality were applied to Ontario, approximately 750 fewer people would die of colorectal cancer each year.

Ultimately all of us will die. The goal of a screening program is to postpone death and provide for quality life-years. The letter writers argue that colorectal cancer screening does not have significant benefits, has no impact on total mortality, carries excessive harms and is too costly. This is an extremely negative perspective that dismisses the strong evidence in favour of screening that has accumulated over the past 25 years.

The lack of a demonstrated impact on overall mortality emphasized by Latosinsky and Budenholzer is understandable considering that colorectal cancer mortality represents only 3% of overall mortality. We do not argue against strategies that would reduce mortality from other causes; individual evidence-based mortality-reducing strategies should be incorporated into an integrated program of wellness. The goal of a screening trial is to reduce mortality from the disease under study without causing any excess mortality. This goal was met by all 3 fecal occult blood test trials. Mandel recently showed that fecal occult blood testing reduces the incidence of, as well as mortality from, colorectal cancer.4 Although Atkin noted that there was a slight increase in the number of deaths from ischemic heart disease in the screening trials,5 this difference was not statistically significant.6

The relative magnitudes of benefits and harms are a personal judgement. We believe the benefits are large; Wright, Brock and Gurekas, and Prasad Koduri see them as small. We agree that all screening programs have harms.3 The intent of our statement regarding harms was to indicate that these harms do not erase the benefits; colorectal cancer screening has a net benefit.7 A study of harms and benefits in a large colorectal cancer screening trial demonstrated no investigation-related mortality.7 Of the 6 colonoscopy complications, 5 were in patients from whom polyps were removed.7 Since polypectomy has been shown to reduce the incidence of colorectal cancer,8 harms were almost entirely in patients who were most likely to benefit. In that trial the number screened to prevent 1 colorectal cancer death was 747 in 7.8 years, and 1 person was harmed for every colorectal cancer death prevented.7 These data refute the argument that the harms of screening equal the benefits. This trial utilized primary care physicians in the community, which addresses the statement by Brock and Gurekas that all trials were in tertiary care settings and thus the findings cannot be extrapolated to community settings.

We agree with Latosinsky that colorectal cancer screening is costly, but so is the management of advanced colorectal cancer. Colorectal cancer screening has been shown to be cost-effective in the United States;3 Ontario needs to determine whether this is true for its population. We certainly agree that people living in Ontario should be given the facts regarding benefits and harms and they should decide if they wish to be screened. We stated in our commentary that “ensuring that patients are fully informed about the harms and benefits of screening is an essential part of the screening strategy.” Adverse consequences of screening must be recognized by community physicians and the public as part of a cancer prevention approach that has an overall benefit.7