Long-Term Estrogen-Only Hormone Therapy Increases Breast Cancer Risk

A new long-term analysis shows that estrogen-only hormone therapy used for more than 10 years increases the risk for breast cancer.

In 2002, a Women’s Health Initiative (WHI) study was stopped early when estrogen plus progestin hormone therapy was shown to increase the risk of invasive breast cancer in healthy postmenopausal women. Later analysis shows the risk of dying from breast cancer also increased.

Because estrogen-only therapy can increase the risk of endometrial cancer, the hormone progestin is added to reduce this risk. In women who have had hysterectomies, estrogen-only hormone therapy is used.

While initial results in another WHI study showed estrogen-only therapy to be safe in regards to breast cancer, a new analysis from the Nurses’ Health Study looked at postmenopausal women who took estrogen-only therapy for longer than 10 years.

Data presented at the American Association for Cancer Research annual meeting showed that women who had used estrogen-only hormone therapy for 10 to about 15 years had a 22 percent increased risk of breast cancer. Women who used this type of hormone therapy for 15 years to about 20 years had a 43 percent increased risk. The risk of death from breast cancer did not appear to increase. Investigators are continuing to research this particular finding.