For postmenopausal women with hormone receptor–positive early breast cancer, extending adjuvant aromatase inhibitor treatment from 5 years to 10 years can increase rates of disease-free survival and decrease incidence of contralateral breast cancer, according to a study published in the New England Journal of Medicine.

However, rates of overall survival were not higher with aromatase inhibitor compared with placebo.

The study included 1,918 postmenopausal women with primary breast cancer who had received 4.5 to 6 years of adjuvant therapy with an aromatase inhibitor. Participants were randomly assigned to receive 2.5 mg of letrozole or placebo orally once a day for an additional 5 years. The mean follow-up was 6.3 years.

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During the follow-up period, there were 165 events involving disease recurrence or the occurrence of contralateral breast cancer (67 in the letrozole group versus 98 in the placebo group) and 200 deaths (100 in each group).

The 5-year disease-free survival rate was 95% in the letrozole group and 91% in the placebo group. The 5-year overall survival rate was 93% in the letrozole group and 94% in the placebo group. The annual incidence rate of contralateral breast cancer was 0.21% in the letrozole group compared with 0.49% in the placebo group. Participants in the letrozole group had a higher frequency of bone-related toxic events (including bone pain, bone fractures, and new-onset osteoporosis) compared with those receiving placebo. No significant differences were observed in quality of life assessment scores between the two groups.

“Ultimately, the decision of whether a patient should receive prolonged therapy with an aromatase inhibitor will depend largely on the extent of its effect on her in terms of toxic effects and quality of life, the extent to which bone mineral density is maintained, as indicated by sequential scans, and the patient’s individual risk of disease recurrence,” the researchers concluded.


  1. Goss PE, Ingle JN, Pritchard KI, et al. Extending aromatase-inhibitor adjuvant therapy to 10 years. N Engl J Med. Published online June 5, 2016; doi:10.1056/NEJMoa1604700.