Rebuttal [CMAJ - September 5, 2000]

Rebuttal
Dr. Marshall responds to Drs. Winawer and Zauber

CMAJ 2000;163(5):548

See also:

Screening for colorectal cancer C.J. Wright; G. Brock, V. Gurekas [Letters]
eLetters

The first argument of Sidney Winawer and Ann Zauber for colon cancer screening¹ is that numerous authoritative bodies have recommended it. In my lifetime of medical practice, "authority" decreed that chest x-ray screening would decrease lung cancer mortality, that median episiotomies would prevent third- and fourth-degree tears and that the only acceptable treatment for breast cancer was radical mastectomy. As a family physician, I'm interested in evidence, not authority.

I agree with Winawer and Zauber that the detection and removal of adenomatous polyps can almost certainly prevent colon cancer; however, fecal occult blood screening does not achieve this goal. Adenomas rarely bleed, and those detected during fecal occult blood screening are incidental findings. The small decrease in colon cancer mortality reported in trials of fecal occult blood screening is due to the detection of early cancers, not to the detection and removal of adenomas.²

In quoting the benefits of colon cancer screening Winawer and Zauber persist in using deceptive relative reduction rates. The actual number of people who have to be screened to prevent one death from colon cancer is very large.³

No clinical trial has reported a decrease in overall mortality in screened populations. Although inadequate power of the studies may be the explanation, screening as the direct or indirect cause of deaths is an equally plausible hypothesis. For example, only a few patients with detected colon cancer or adenomas have to die as a result of surgery to negate any benefit from the screening process.

The results of clinical trials are rarely replicated in community settings. If Ontario undertakes a fecal occult blood screening program, all residents who participate should be aware that they are participating in an experiment.

Public information about colon cancer screening is largely propaganda. "Get tested [for colon cancer] and save your life!" appeared on the cover of the Mar. 13, 2000, edition of Time magazine; one sentence in the ensuing 6-page article alluded to the remote possibility of bowel perforation during colonoscopy.⁴ The Web site "Screen for Life" (www.cdc.gov/cancer/screenforlife), launched by the US Centers for Disease Control and Prevention, the Health Care Financing Administration and the National Cancer Institute, is blatantly promotional; not one mention of adverse effects appears on the site.

Society is becoming more and more obsessed by disease. Every new screening program generates fear. Population-based screening for colon cancer has not been proven to save lives, but it will almost certainly decrease our quality of life. Now is not the time to screen.

References

    1.    Winawer SJ, Zauber AG. Colorectal cancer screening: Now is the time. CMAJ 2000;163(5):543-4.

    2.    Ahlquist DA. Fecal occult blood testing for colorectal cancer: Can we afford to do this? [review] Gastroenterol Clin North Am 1997;26:41-55.

    3.    Towler B, Irwig L, Glasziou P, Kewenter J, Weller K, Siagy C. A systematic review of the effects of screening for colorectal cancer using the faecal occult blood test, Hemoccult. BMJ 1998;317:559-65. [MEDLINE]

    4.    Gorman C. Katie's crusade. Time 2000;155(10):40-6.