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Colorectal Cancer Health Center

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Colorectal Cancer Prevention (PDQ®): Prevention - Health Professional Information [NCI] - Overview



Based on solid evidence, harms of ASA use include excessive bleeding, including gastrointestinal bleeds and hemorrhagic stroke.

Magnitude of Effect: The estimated average excess risk of upper gastrointestinal complications is 10 to 30 per 1,000 people for a period of 10 years, on the higher end for men and on the lower end for women. Risk increases with age.

Study Design: Evidence obtained from large databases.[15,20]
Internal Validity: Good.
Consistency: Good.
External Validity: Good, data from national databases.

Hormone therapy (estrogen plus progestin)

Based on solid evidence, combined hormone therapy (conjugated equine estrogen and progestin) decreases the incidence of invasive CRC.[21]

Based on fair evidence, combination conjugated equine estrogen and progestin has little or no benefit in reducing mortality from CRC. Data from the Women's Health Initiative (WHI), a randomized, placebo-controlled trial evaluating estrogen plus progestin, with a mean intervention of 5.6 years and a follow-up of 11.6 years showed that women taking combined hormone therapy had a statistically significant higher stage of cancer (regional and distant) at diagnosis but not a statistically significant number of deaths from CRC compared with women taking the placebo.[21]

Magnitude of Effect: There were fewer CRCs in the combined hormone therapy group than in the placebo group (0.12% vs. 0.16%; HR = 0.72; 95% CI, 0.56-0.94). A meta-analysis of cohort studies observed a RR of 0.86 (95% CI, 0.76-0.97) for incidence of CRC associated with combined hormone therapy.

There were 37 CRC deaths in the combined hormone therapy arm compared with 27 deaths in the placebo arm (0.04% vs. 0.03%; HR 1.29; 95% CI, 0.78-2.11).

  • Study Design: Randomized controlled trial and cohort studies
  • Internal Validity: Good.
  • Consistency: Good for effect on incidence; N/A for effect on mortality; results were based on one trial.
  • External Validity: Good.

Estrogen-only therapy


Based on fair evidence, conjugated equine estrogens do not affect the incidence of, or survival from, invasive CRC.[22]

Magnitude of Effect: N/A.

Study Design: One randomized controlled trial.
Internal Validity: Good.
Consistency: N/A.
External Validity: Good.
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