In addition, aromatase inhibitors -- drugs known as Arimidex, Aromasin and Femara -- are less likely to cause blood clots and vaginal bleeding than other hormone treatments, said review co-author Judith Bliss of the Institute of Cancer Research in London.
The review analyzed 30 studies involving the treatment of advanced breast cancer, encompassing more than 10,000 postmenopausal women.
Bliss and colleagues were surprised at how few of the reviewed studies presented data on overall survival for women taking aromatase inhibitors. "Survival data was only available for about half of the women," Bliss said.
The available data showed an 11 percent reduction in the risk of death compared to women not receiving aromatase inhibitors.
The review appears in the current issue of The Cochrane Library, a publication of The Cochrane Collaboration, an international organization that evaluates medical research. Systematic reviews draw evidence-based conclusions about medical practice after considering both the content and quality of existing medical trials on a topic.
The treatment of advanced breast cancer in women who have gone through menopause usually involves a combination of surgery, radiation, chemotherapy, hormonal and biological therapies. In many breast cancers, estrogen stimulates tumor growth. Aromatase inhibitors work by limiting a woman's production of estrogen.
Several aromatase inhibitors, including anastrozole (Arimidex), exemestane (Aromasin) and letrozole (Femara) have been available for clinical use for the past decade or so.
Other breast cancer treatments that also affect estrogen include tamoxifen and progestins. Tamoxifen is the most widely used hormonal treatment in advanced breast cancer; however, it carries a risk of blood clots and other rare but potentially serious side effects.
Bliss said that the review found very little reliable data in the trials comparing the effectiveness of the different available aromatase inhibitors. "The promotion of one individual drug over another is not evidence-based and should be avoided," the authors said.
In general, women taking aromatase inhibitors had about the same risk of experiencing hot flashes as those receiving tamoxifen. However, they reported more nausea, vomiting and diarrhea when compared to patients receiving the progestin drug megestrol acetate and to a lesser extent, when compared with patients receiving tamoxifen.
Patients taking aromatase inhibitors had a decreased risk of vaginal bleeding and blood clots compared to those using other hormonal therapies.
Safety data were difficult to analyze, Bliss said: "The picture is patchy due to poor quality of adverse event reporting and different study endpoints," in the various trials.
However, "the review findings do confirm modest, but real therapeutic benefits from the use of aromatase inhibitors in a variety of clinical settings," Bliss said.
Edith Perez, M.D., an oncologist with the Multidisciplinary Breast Cancer Program at the Mayo Clinic in Jacksonville, Fla., said, "The results of the review are not a surprise. These are good drugs and they have positively impacted the lives of patients with breast cancer." Perez is not associated with the review.
Perez believes that aromatase inhibitors are the first drug of choice for hormonal treatment of advanced breast cancer in postmenopausal women. "They have a slightly improved efficacy over tamoxifen, and they have a much lower rate of blood clots in the legs and lungs," she said. "Aromatase inhibitors carry almost no risk of uterine cancer, and while that rarely happens with tamoxifen, it does happen."
On the other hand, Perez said that aromatase inhibitors do carry a risk of increased joint aches and, more importantly, may cause bone loss. "The majority of patients do very well but we recommend patients have bone density tests before using these drugs. I would probably not use aromatase inhibitors in a patient with severe osteoporosis."
While per-tablet cost of aromatase inhibitors is higher than tamoxifen, Perez said that they are still cost-effective because they have fewer side effects requiring treatment and they result in increased overall survival.
"It's no question that these drugs are better for patients when compared with other hormone therapies," Perez said.
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