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Estrogen-Progestin Combination May Increase Risk for Breast Cancer

Several recent studies have indicated that breast cancer risk increases with estrogen use, particularly long-term use. These investigators analyzed data on 46,355 women from the Breast Cancer Detection Demonstration Project to determine whether combined use of estrogen-progestin increased risk beyond that of estrogen alone.

Increased breast cancer risk was restricted to current and recent (within 4 years) hormone use (risk ratio, 1.2 and 1.4 for estrogen only and estrogen-progestin, respectively). The relative risk for breast cancer increased by 1% per year for estrogen use and 8% per year for estrogen-progestin use. Notably, the risk increased with duration of use, but only among lean women (BMI less than 24.4 kg/m²), with increases in relative risk of 3% and 12%, respectively, with estrogen-only and estrogen-progestin use.

Comment: This study suggests that the addition of progestin to estrogen increases breast cancer risk in current and recent users. Because the association was found only in lean women (less than 120 lbs for an average-height woman), these findings can be generalized only to a small percentage of patients: lean women who take hormone therapy long-term. Future randomized clinical trials will resolve questions about the impact of hormone therapy on breast cancer risk. For now, clinicians should explain that in some patients hormone therapy may marginally increase breast cancer risk, and women should weigh this risk against the known benefits of hormone therapy.

— SD Gharib

Published in Journal Watch Women's Health March 1, 2000

Citation(s):

Schairer C et al. Menopausal estrogen and estrogen-progestin replacement therapy and breast cancer risk. JAMA 2000 Jan 26 283 485-491.

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Willett WC et al. Postmenopausal estrogens -- Opposed, unopposed, or none of the above. JAMA 2000 Jan 26 283 534-535.

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