Exemestane is better than tamoxifen in years 2-5 after breast cancer

Question Does exemestane improve outcomes in patients with breast cancer when treatment with it starts 2-3 years after diagnosis?

Synopsis Tamoxifen is the current standard of care for the treatment of oestrogen receptor positive breast cancer in postmenopausal women. Exemestane is an aromatase inhibitor (they block the conversion of androgens to oestrogen) and may be superior to tamoxifen in patients with metastatic disease. After 2-3 years of tamoxifen therapy, patients were randomised to receive exemestane 25 mg daily (n = 2380) or tamoxifen 20 mg daily (n = 2362) to complete a 5 year course of therapy. All of the women were postmenopausal, had normal renal and liver function, and had an oestrogen receptor positive primary breast cancer. Allocation was concealed and analysis was by intention to treat. Patients were re-evaluated regularly. The primary outcome was disease-free survival. The number of patients with death, contralateral breast cancer, or recurrence was lower in the exemestane group (183 v 266 (7.8% v 11.2%); P < 0.001). After three years, the likelihood of disease-free survival was 91.5% in the exemestane group and 86.8% in the tamoxifen group (absolute risk reduction 4.7%; number needed to treat for 3 years = 21.3). There were fewer deaths in the exemestane group, but this difference was not statistically significant (93 v 106). The risk of contralateral breast cancer was lower in the exemestane group (hazard ratio 0.44; 95% confidence interval 0.20 to 0.98). Exemestane caused more arthralgias and diarrhoea, but fewer thromboembolic events, less vaginal bleeding, and fewer muscle cramps than tamoxifen.

Bottom line Exemestane improves outcomes for postmenopausal women with oestrogen receptor positive breast cancer when given for 2-3 years after 2-3 years of treatment with tamoxifen.

Level of evidence 1b (see www.infopoems.com/levels.html). Individual randomised controlled trials (with a narrow confidence interval).