Estrogen and colorectal cancer incidence and mortality

• Published in: Cancer 2015-09, Vol.121 (18), p.3261-3271
• Main Authors: Lavasani, Sayeh, Chlebowski, Rowan T., Prentice, Ross L., Kato, Ikuko, Wactawski‐Wende, Jean, Johnson, Karen C., Young, Alicia, Rodabough, Rebecca, Hubbell, F. Allan, Mahinbakht, Ali, Simon, Michael S.
• Format: Article
• Language: English
• Subjects: Adenocarcinoma - epidemiology; Aged; colorectal cancer; Colorectal Neoplasms - epidemiology; Double-Blind Method; estrogen; Estrogen Replacement Therapy - methods; Estrogens - therapeutic use; Estrogens, Conjugated (USP) - therapeutic use; Female; Follow-Up Studies; Humans; Incidence; Middle Aged; mortality; postmenopausal women
• ISSN: 0008-543X; 1097-0142
• DOI: 10.1002/cncr.29464

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