ASCO guidelines recommend aromatase inhibitors

New guidelines from the American Society of Clinical Oncology (ASCO) recommend that postmenopausal women with hormone receptor-positive breast cancer take an aromatase inhibitor to reduce the risk of recurrence.

An expert panel revised existing ASCO guidelines based on a systematic review of the literature (including 12 major trials) on endocrine therapy for women with hormone-receptor positive disease. The experts concluded that most postmenopausal women with the disease should take an aromatase inhibitor (AI) at some point, either as the initial adjuvant therapy or after taking tamoxifen. The guideline recommends that the switch from tamoxifen to an AI be made after two to three years, but the experts noted that switching after five years is also supported by the evidence. AI therapy can be continued for up to five years.

The three different AIs that are currently available show no clinically important differences in effectiveness, the experts concluded. They also compared side effects of the AIs and tamoxifen, finding them to be mild overall, but noting that AIs may reduce the chances of blood clots and uterine cancer but increase the risk of osteoporosis and fractures compared to tamoxifen. Patients who are intolerant of one AI may be advised to switch to another AI or tamoxifen.

Women who are pre- or peri-menopausal should not take an AI, the experts said. For those women, the guidelines recommend five years of tamoxifen. For post-menopausal women, the choice of whether and when to incorporate AI therapy should be based on adverse event profiles and patient preferences, the guidelines said. No biomarkers have been proven effective at determining which treatment strategy is best.

The guidelines also called for additional research on improving adherence to therapy, the optimal time to switch from one therapy to another, the role of drug metabolism and pharmacogenetics, and markers of subtypes of hormone-receptor positive cancer than may respond better to certain therapies. The guidelines were published online July 12 by the Journal of Clinical Oncology. A press release is also online.