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abstract
BACKGROUND
The
preponderance of observational studies describe an association between
the use of estrogen alone and a lower incidence of colorectal cancer. In
contrast, no difference in the incidence of colorectal cancer was seen
in the Women's Health Initiative (WHI) randomized, placebo-controlled
trial with estrogen alone after a mean intervention of 7.1 years and
cumulative follow-up of 13.2 years. This study extends these findings by
providing detailed analyses of the effects of estrogen alone on the
histology, grade, and stage of colorectal cancer, relevant subgroups,
and deaths from and after colorectal cancer.
METHODS
The
WHI study was a randomized, double-blind, placebo-controlled trial
involving 10,739 postmenopausal women with prior hysterectomy.
Participants were assigned to conjugated equine estrogen at 0.625 mg/d
(n = 5279) or a matching placebo (n = 5409). Rates of colorectal cancer
diagnoses and deaths from and after colorectal cancer were assessed
throughout the study.
RESULTS
Colorectal
cancer rates in the estrogen-alone and placebo groups were comparable:
0.14% and 0.12% per year, respectively (hazard ratio [HR], 1.13; 95%
confidence interval [CI], 0.83-1.58; P = .43). Bowel screening
examinations were comparable between the 2 groups throughout the study.
The grade, stage, and location of colorectal cancer did not differ
between the randomization groups. There were more colorectal cancer
deaths in the estrogen-alone group (34 [0.05%] vs 24 [0.03%]; HR, 1.46,
95% CI, 0.86-2.46; P = .16), but the difference was not
statistically significant. The colorectal cancer incidence was higher
for participants with a history of colon polyp removal in the
estrogen-alone group (0.23% vs 0.02%; HR, 13.47; nominal 95% CI,
1.76-103.0; P < .001).
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