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Timing, type of hormone therapy linked to breast cancer incidence

Beral V. J Natl Cancer Inst. 2011;103:1-10.

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The timing of hormone therapy may reduce risks for breast cancer, according to results of a prospective study. Researchers found that type of hormone therapy used, time between menopause and first use, and duration of therapy were all independent effects among current hormone therapy users.

“Some of these findings confirm what is already well known, for example, that current users of estrogen-progestin preparations are at the greatest risk of breast cancer and that the associated risk increases with duration of use,” the researchers wrote.

The study included prospective information regarding hormone therapy use for 1,129,025 postmenopausal women in the United Kingdom. The researchers compared the estimated RR for breast cancer among hormone therapy users and those who never used hormone therapy, and they calculated standardized incidence rates. Follow-up was 4.05 million woman-years.

Incident breast cancers occurred among 15,759 women, 7,107 of whom were current hormone therapy users, during follow-up. Breast cancer occurrence was higher among hormone therapy users, but within years of stopping therapy, incidence decreased to that of a never user. Among current users, the RR for disease was higher if therapy began before or shortly after menopause compared with being started longer after menopause; this was true for both estrogen-only and estrogen-progestin formulas (P_{heterogeneity} <.001).

Breast cancer risk was slightly increased or not increased at all among estrogen-only users who began therapy 5 or more years after menopause (RR=1.05; 95% CI, 0.89-1.24); however, the risk was significantly increased if therapy began before menopause or less than 5 years after menopause (RR=1.43; 95% CI, 1.35-1.51). According to the researchers, the trend was similar among estrogen-progestin users if use began 5 or more years after menopause (RR=1.53; 95% CI, 1.38-1.70) vs. before or less than 5 years after menopause (RR=2.04; 95% CI, 1.95-2.14).

The annual standardized incidence rate for disease at 50 to 59 years of age was 0.3% (95% CI, 0.29-0.31) for never users, 0.43% (95% CI, 0.42-0.45) among current users of estrogen-only formulas and 0.61% (95% CI, 0.59-0.64) among current users of estrogen-progestin formulas who began therapy less than 5 years after menopause.

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