Ask the Care Team
What is the role of aromatase inhibitors for women with breast cancer?
Tamoxifen, an anti-estrogen therapy, has long been the standard treatment for postmenopausal women with hormone receptor-positive breast cancer. Based on the results of large trials, a five-year course of therapy was felt to be optimal. Aromatase inhibitors are drugs that decrease estrogen levels in postmenopausal women, and, like tamoxifen, they can reduce a woman's risk of recurrence following surgery for early, hormone-dependent breast cancer.
Over the past three years, five large clinical trials have shown that in postmenopausal women with hormone receptor-positive, Stage I and II breast cancer, the aromatase inhibitors can add to the benefits seen with tamoxifen. As a result, many doctors are advising women to consider taking one of the three commercially available aromatase inhibitors: Arimidex, Aromasin, and Femara.
Eric Winer, MD, director of the Breast Oncology Center at Dana-Farber, chaired a panel of the American Society of Clinical Oncology (ASCO) that issued a recommendation on aromatase inhibitors late last year. Harold Burstein, MD, a clinician and investigator in the Breast Oncology Center also served on the panel.
"The ASCO recommendation indicates that postmenopausal women with hormone-dependent breast cancer should strongly consider the use of an aromatase inhibitor at some point during the course of therapy," explains Dr. Winer. "There are two strategies that are reasonable at this time—either tamoxifen followed by an aromatase inhibitor, or treatment with an aromatase inhibitor alone."
"For some women who are at very low risk of recurrence or have side effects with the aromatase inhibitors, treatment with tamoxifen alone certainly remains a possibility," he says.
Aromatase inhibitors are contraindicated in women who have functioning ovaries, and they are ineffective in women whose tumors are estrogen- and progesterone-negative. The drugs are being tested in women with ductal carcinoma in situ, and in women who are at increased breast cancer risk.
Unlike tamoxifen, aromatase inhibitors do not increase the risk of blood clots or endometrial cancer. But they can cause osteoporosis, so additional drugs may be prescribed to counter the increased risk of bone fractures. The side effects of aromatase inhibitors beyond five years are not known.
Ongoing studies will compare the three aromatase inhibitors against each other, and compare different treatment sequences. According to Dr. Burstein: "We need to figure out if some patients will benefit from tamoxifen followed by an aromatase inhibitor, while others may do better with an aromatase inhibitor alone."
