Timing of Hormonal Therapy Can Affect Level of Breast Cancer Risk

Timing of Hormonal Therapy Can Affect Level of Breast Cancer Risk

Women may be at greater risk for breast cancer if they start hormonal therapy before or soon after menopause, according to a large prospective study. Women who begin therapy 5 or more years after menopause are at less risk.

Researchers used Cox regression to estimate adjusted relative risks (RRs) of breast cancer from data provide by 1,129,025 postmenopausal women in the United Kingdom. In current users (n = 7107) risk was greater if hormonal therapy began before or soon after menopause for women taking both estrogen-only and estrogen-progestin formulations (P_{heterogeneity}<.001). Estrogen-only formulations conferred higher risk if taken <5 years after menopause (RR, 1.43; 95% confidence interval [CI], 1.35-1.51), as did estrogen-progestin formulations (RR, 2.04; 95% CI, 1.95-2.14). Little or no increase in risk occurred if use began ≥5 years after menopause (RR, 1.05; 95% CI, 0.89-1.24; and RR, 1.53; 95% CI, 1.38-1.70, respectively).

For users, the risk drops 2 years after hormonal therapy is ceased. With up to 14 years of posttherapy follow-up, the risk remained similar to that of never users (RR, 0.99; 95% CI, 0.93-1.05; n = 1098).

The complete findings are published online in the Journal of the National Cancer Institute.

Timing of Hormonal Therapy Can Affect Level of Breast Cancer Risk

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