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Cancer Causes Control. 2001 Jun;12(5):405-10.

Colorectal cancer following tamoxifen therapy for breast cancer (United States).

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Division of Public Health Sciences, Fred Hutchinson Cancer Research Center, Seattle, WA, USA.



An analysis combining data from several clinical trials has raised concern that tamoxifen therapy may increase the risk of a subsequent colorectal malignancy. We conducted a nested case-control study to test this hypothesis.


A cohort of women diagnosed with breast cancer in 1978-1992 was identified from the western Washington population-based cancer registry. Cases included women who subsequently developed colorectal cancer prior to 1995. Controls were a random sample of the cohort who did not develop a second primary malignancy, matched to cases on age, stage, and year of initial cancer diagnosis. Tamoxifen use was ascertained by medical record abstraction and physician questionnaires.


Thirty-six percent of the 122 cases for whom information could be obtained received tamoxifen versus 38% of 194 controls. Relative to non-users and adjusted for receipt of other therapies, there was no increased risk of colorectal cancer associated with tamoxifen use in general (matched odds ratio [mOR] = 0.9, 95% CI 0.6-1.6), longer durations of use (for > or =37 months, mOR = 0.8, 95% CI 0.4-1.9), higher cumulative doses of therapy (for > or =15 g, mOR = 0.8, 95% CI 0.4-1.6), or use that started at least 5 years prior to the end of study follow-up (mOR = 1.1, 95% CI 0.3-3.7).


We found no overall increased risk for colorectal cancer among tamoxifen users.

[Indexed for MEDLINE]

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