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Minnesota Colon Cancer Control Study

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This Citizendium article provides a structured summary a previously published research study. There are two purposes for summarizing previously published research articles in a standard format:

  1. Increase the reader's ability to understand the contents of the article. Research has shown that physicians have difficulty reading medical research articles. Physicians have trouble quantifying benefits of treatments and diagnostic tests [1][2][3]. A specific example of this difficulty is that physicians have difficulty interpreting relative versus absolute effects [4]
  2. Provide building blocks that Wiki authors can reference to when writing about this topic (in this case, screening for colorectal cancer). The format below is based on prior work about "critically appraised topics" (PMID 15588311, PMID 15579428, PMID 15204609, PMID 15105349, PMID 14728311, PMID 11702349).

Contents

"Reducing mortality from colorectal cancer by screening for fecal occult blood. Minnesota Colon Cancer Control Study"

This is a structured summary of a research study entitled "Reducing mortality from colorectal cancer by screening for fecal occult blood. Minnesota Colon Cancer Control Study"[5] originally published in 1993 in the New England Journal of Medicine. Click here to see the original abstract.

Summary of the original article

A randomized controlled trial of 46,551 participants aged 50 to 80 years were randomized to one of:

  • screening for colorectal cancer once a year using the stool guaiac test. Per the text of the paper, 'six guaiac-impregnated paper slides with two smears from each of three consecutive stools'.
  • screening every two years using the stool guaiac test. Per the text of the paper, 'six guaiac-impregnated paper slides with two smears from each of three consecutive stools'.
  • control group.

Results

These results are limited to the annually screened group versus the control group as the effect of biennial screening was not significant.

Cross tabulation
Deaths from
colorectal cancer
Alive Totals
Annual screening 82 15488 15570
Control 117 15277 15394
Totals 199 30765
(this table was reconstructed by using the totals in Table 1 of the article and using the outcomes in Table 4 of the article)

The numbers in the cross tabulation lead to the following event rates:

Event rates for colorectal cancer mortality
Group Rate Confidence interval
Annual screening 0.588% (4.61 to 7.15)
Control 0.883% 7.26 to 10.40)

These event rates lead to the following measures of efficacy:

Measures of Efficacy
Absolute risk reduction 0.3%
Number needed to treat 339
Relative risk reduction 33.4%

Per the authors, 'the rate in the annually screened group, but not in the biennially screened group, was significantly lower than that in the control group'. The p-value is not in the article.

Are the results significant?

  1. To assess whether the results are statistically significant, not only the p-value is important, but factors such as publication bias that might influence the p-value are important. To alter the a priori estimate of the null hypothesis, click here. (this paragraph needs to be much more user friendly)
  2. Clinical significance must also be considered. For example, the results may be statistically significant, but the number needed to treat may reveal that too few patients will benefit for patients to be willing to accept expense and effort of the treatment.

How will these result be changed in patients at higher or lower risk of the outcome?

The risk of death from colorectal cancer in this study is 0.883% in the unscreened group. For patients who have risk factors that make their risk higher or lower than this number, their benefit will be higher or lower. Use [this link] to adjust the baseline risk.

Follow-up

The results of the is study after 18 years of follow-up have been published.[6]

References

  1. Bergman D, Pantell R (1986). "The impact of reading a clinical study on treatment decisions of physicians and residents". J Med Educ 61 (5): 380-6. PMID 3701813.
  2. Beasley B, Woolley D (2002). "Evidence-based medicine knowledge, attitudes, and skills of community faculty". J Gen Intern Med 17 (8): 632-9. PMID 12213145.
  3. Berwick D, Fineberg H, Weinstein M (1981). "When doctors meet numbers". Am J Med 71 (6): 991-8. PMID 7315859.
  4. Bucher H, Weinbacher M, Gyr K (1994). "Influence of method of reporting study results on decision of physicians to prescribe drugs to lower cholesterol concentration". BMJ 309 (6957): 761-4. PMID 7950558.
  5. Mandel J, Bond J, Church T, Snover D, Bradley G, Schuman L, Ederer F (1993). "Reducing mortality from colorectal cancer by screening for fecal occult blood. Minnesota Colon Cancer Control Study". N Engl J Med 328 (19): 1365-71. PMID 8474513. "
  6. Mandel J, Church T, Bond J, Ederer F, Geisser M, Mongin S, Snover D, Schuman L (2000). "The effect of fecal occult-blood screening on the incidence of colorectal cancer". N Engl J Med 343 (22): 1603-7. PMID 11096167.
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