Extending Aromatase-Inhibitor Adjuvant Therapy to 10 Years

Authors: Goss, P.E. et. al.

Source: NEJM, doi:10.1056/NEJMoa1604700

www.nejm.org/doi/full/10.1056/NEJMoa1604700#t=article

This study (called MA.17R) was an extension of previous work that showed benefits among ER positive breast cancer patients when adjuvant (postoperative) therapy was extended from 5 to 10 years. There is data to support a woman’s taking tamoxifen for 10 years and for taking tamoxifen for 5 years followed by an aromatase inhibitor for five years. Many patients do take an aromatase inhibitor for 10 years, but there has been no specific data to support this practice.

Participants were over 1900 postmenopausal women who completed primary treatment for ER positive breast cancer and had taken 4.5-6 years of an aromatase inhibitor. Within 2 years of ending that treatment, they were randomized to either placebo or letrozole daily for another 5 years. The women were followed regularly with physical examination, blood work, mammography, bone density tests and assessment of drug toxicity. Quality of life was also assessed.  Median follow up was 6.3 years.

The rates of breast cancer recurrence and development of cancer in the opposite breast were higher in the women on placebo. These results translated into a higher disease-free survival in the letrozole group vs. placebo: 95% vs. 91%, respectively. This difference was statistically significant.

Women on letrozole experienced more bone mineral density loss. This group also reported worse quality of life over time. Specifically, body pain was more frequently described. However, at the end of 4 and 5 years, this complaint was higher among the placebo group. For both groups, few women stopped the medication because of side effects.

Interestingly, over 60% of participants had taken 5 years of tamoxifen prior to their initial aromatase inhibitor therapy. This did not result in a difference in disease-free survival.

Overall survival at 6.3 years was equivalent between both groups.

This study supports the use of 10 years of aromatase inhibitor therapy with letrozole. This regimen has an impact on disease-free survival with modest impairment of quality of life.