Timing of Hormone Therapy Influences Breast Cancer Risk

THURSDAY, Feb. 3 (HealthDay News) -- For women taking postmenopausal hormone therapy, breast cancer risk is greater among users of estrogen-progestin formulations, and those who begin treatment earlier, according to a study published online Jan. 28 in the Journal of the National Cancer Institute.

Valerie Beral, F.R.S., from the University of Oxford in the United Kingdom, and colleagues analyzed data from 1,129,025 postmenopausal women. The adjusted relative risk for hormone therapy users compared to women who never used hormone therapy was assessed, and standardized incidence rates were calculated.

The investigators found an increased incidence of breast cancer among women currently using hormone therapy, which was reduced some years after stopping therapy. The relative risk of breast cancer increased when women started hormone therapy before or soon after menopause, compared with after a longer gap. Current users of estrogen-only or estrogen-progestin formulations had little or no risk when starting treatment five or more years after menopause, but had a statistically increased risk if treatment began after less than five years. The annual standardized breast cancer rate for women aged 50 to 59 was 0.30 percent if women never used hormone therapy. Among women who began hormone treatment less than five years after menopause, the rates were 0.43 percent for current estrogen-only users and 0.61 percent for current estrogen-progestin users.

"Among current users of hormonal therapy, there were independent effects of the type of hormonal therapy used, the time between menopause and first use of hormonal therapy, and the duration of hormonal therapy use," the authors write.

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