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


METHODS
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.


RESULTS
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).


CONCLUSIONS
We found no overall increased risk for colorectal cancer among tamoxifen users.
Cook
L S
LS
Division of Public Health Sciences, Fred Hutchinson Cancer Research Center, Seattle, WA, USA. cook@ucalgary.ca
Weiss
N S
NS
Pharris-Ciurej
N
N
Schwartz
S M
SM
White
E
E
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001943:Breast Neoplasms / Q000188:drug therapy*; D015331:Cohort Studies; D015179:Colorectal Neoplasms / Q000139:chemically induced* / Q000556:secondary*; D005260:Female; D006801:Humans; D008875:Middle Aged; D011159:Population Surveillance; D012307:Risk Factors; D013629:Tamoxifen / Q000627:therapeutic use*; D016896:Treatment Outcome; D014481:United States
D013629:Tamoxifen