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Exemestane reduces breast cancer risk in high-risk postmenopausal women

Clinical Question:
Does exemestane reduce the risk of breast cancer without causing other important harms?

Bottom Line:
Exemestane appears to safely reduce the risk of breast cancer in high-risk postmenopausal women. The number needed to treat (NNT) of 278 per year is more attractive over time: Consider a woman taking the drug for 5 years (NNT = 56) or 10 years (NNT = 28). At at least $300 per month, it would cost at least US$1 million to prevent one case of invasive breast cancer, and since not everyone with breast cancer dies, it would cost much more to prevent one death. (LOE = 1b)

Reference:
Goss PE, Ingle JN, Alés-Martinez JE, et al, for the NCIC CTG MAP.3 Study Investigators. Exemestane for breast-cancer prevention in postmenopausal women. N Engl J Med 2011;364(25):2381-2391.  [PMID:21639806]

Study Design:
Randomized controlled trial (double-blinded)

Funding:
Industry + govt

Allocation:
Uncertain

Setting:
Outpatient (any)

Synopsis:
Exemestane (Aromasin) is an aromatase inhibitor that suppresses estrogen levels and may therefore reduce the risk of breast cancer, especially in higher-risk women. In this study, the authors identified 4560 postmenopausal women at increased risk for breast cancer because of 1 of 4 risk factors (Gail score >= 1.66%; age 60 years or older; prior ductal or lobular hyperplasia; or prior lobular or ductal carcinoma in situ). The mean age of the women was 62 years (range = 38 - 88 years) and two thirds were 60 years or older; 94% were white. Women with a history of invasive breast cancer were excluded. Women were randomized (allocation concealed) to receive either exemestane 25 mg once daily or placebo (there was also a separate randomization to celecoxib or placebo). Patients were followed up for a median of 36 months, and analysis was by intention to treat. At the end of the study, the annual incidence of invasive breast cancer was 0.19% in the exemestane group and 0.55% in the placebo group (absolute risk reduction = 0.36; P = .002; NNT = 93 for 3 years to prevent 1 breast cancer). More women in the exemestane group discontinued treatment (32.8% vs 28.7%); the greatest increase in a side effect in the exemestane group was, not surprisingly, hot flashes. There was no significant difference in rates of fracture, osteoporosis diagnosis, cardiovascular events, or solid tumors. There were 19 deaths in each group and no difference in quality of life scores.

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