ASCO Adds Aromatase Inhibitor to Breast Cancer Prevention Options in Postmenopausal Women

September 2013, Vol 4, No 7

An aromatase inhibitor has joined tamoxifen (Nolvadex) and the selective estrogen receptor (ER) modulator raloxifene hydrochloride (Evista) as chemoprevention for women who are at an increased risk for breast cancer, according to the recent update of the American Society of Clinical Oncology (ASCO) practice guideline (Visvanathan K, et al. J Clin Oncol. 2013;31:2942-2962).

Tamoxifen and raloxifene have been recommended for breast cancer risk reduction since the ASCO clinical guideline was introduced in 1999, and remained options in the 2002 and 2009 updates. However, the 2009 update specifically excluded aromatase inhibitors as an option for chemoprevention.

After a systematic review of randomized trials and meta-analyses, the guideline committee, cochaired by Kala Visvanathan, MD, MHS, Associate Professor of Epidemiology and Oncology, Johns Hopkins Medical Institutions, Baltimore, MD, concluded that “exemestane (25 mg per day for 5 years) should also be discussed...for BC [breast cancer] risk reduction.”

Table
Table: Key Pharmacologic Interventions for Breast Cancer Risk Reduction.
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The results of a recent randomized, placebo-controlled clinical trial showed that high-risk postmenopausal women who received prophylactic therapy with exemestane (Aromasin) had almost a 70% lower risk for breast cancer compared with high-risk women receiving placebo. The new exemestane recommendation comes with some qualifiers that limit its use to “ER-positive breast cancer, in postmenopausal women age ≥35 years with a 5-year projected breast cancer absolute risk ≥1.66%, according to the NCI [National Cancer Institute] Breast Cancer Risk Assessment Tool (or equivalent measures), or with LCIS [lobular carcinoma in situ] or atypical hyperplasia” (Table).

“Exemestane should not be used for breast cancer risk reduction in premenopausal women,” continued the guideline authors. “Discussions with patients and healthcare providers should include both the risks and benefits of each agent under consideration.”

The panel noted that exemestane does not have a US Food and Drug Administration–approved indication for use as a chemopreventive agent. The drug is currently indicated as adjuvant therapy for early breast cancer and for the treatment of advanced breast cancer. Furthermore, premenopausal women should not use exemestane for breast cancer chemoprevention.

The guideline notes several contraindications for each of the agents (Table). The committee found the data insufficient to make a recommendation about other aromatase inhibitors, including anastrozole (Arimidex). The results of an ongoing randomized, placebo-controlled clinical trial with this drug may help guide the decision-making in the future.

Tamoxifen and raloxifene have the most favorable risk-benefit profile in women at the highest risk for breast cancer, the panel noted.

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