Estrogen-suppressing drugs called aromatase inhibitors have become an important part of treatment for  postmenopausal breast cancer patients who have disease with estrogen receptors.

But like all drugs, the three aromatase inhibitors on the market have side effects, so researchers continue to study which women benefit most, and how long therapy should last.

Several studies presented this week at the annual San Antonio Breast Cancer Symposium have shed more light on the risk-benefit tradeoffs:

Aromatase inhibitors, which block an enzyme that turns androgen into small amounts of estrogen,  are known to cause more heart problems than tamoxifen, an older drug that binds directly to estrogen receptors in the breast. A study led by the University of Minnesota points to a reason for the inhibitors' cardiac effects: these drugs reduce the ability of blood vessels to relax and contract. The study was small -- 25 healthy postmenopausal women compared with 36 breast cancer patients taking an aromatase inhibitor -- but showed a clear link between the drug and reduced vessel elasticity, higher blood pressure, and greater inflammation.

For patients treated with chemotherapy before surgery to reduce their tumor size, adding an aromatase inhibitor may not help, according to a study sponsored by the National Cancer Institute. While previous studies suggested the addition might be beneficial, in the new study of 315 patients, the percentage who saw their tumors completely disappear was statistically the same with or without an aromatase inhibitor. Study leader Mothaffar Rimawi, a breast oncologist at Baylor College of Medicine, said in a press release, "Discovering which patients need more therapy and which need less is crucial."

A large, multi-center clinical trial showed that taking the aromatase inhibitor letrozole for an extended period was not clearly beneficial in postmenopausal women with early-stage breast cancer. The  study of 3,900 women found that 10 years of letrozole was not significantly better than five years in terms of their disease-free survival or overall survival.

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