Among postmenopausal women who complete five years of tamoxifen for the treatment of early-stage breast cancer, an additional five years of treatment with the aromatase inhibitor Femara® (letrozole) may improve overall survival. These results were published in the Journal of Clinical Oncology.

The majority of breast cancers are hormone receptor-positive. These cancers are stimulated to grow by the circulating female hormones estrogen and/or progesterone. Treatment of hormone receptor-positive breast cancer often involves hormonal therapies that suppress or block the action of estrogen. These therapies include tamoxifen as well as drugs known as aromatase inhibitors, such as Femara. Tamoxifen acts by blocking estrogen receptors, whereas aromatase inhibitors suppress the production of estrogen in postmenopausal women. Hormonal therapy is often given for five years.

The MA.17 trial was designed to assess extended hormonal therapy among postmenopausal women with early-stage, hormone receptor-positive breast cancer. Women who had very recently completed five years of tamoxifen were assigned to receive an additional five years of treatment with Femara or a placebo.

Early results from the study showed that extended therapy with Femara reduced the risk of cancer recurrence, and women in the placebo group were offered Femara. At the time of that early analysis, it was not possible to tell whether extended treatment with Femara affected overall survival; longer follow-up was needed.

Study participants have now been followed for over five years. The effect of Femara on overall survival was assessed using statistical techniques that attempted to account for the fact that many women in the placebo group started taking Femara after the early results were announced.

  • As was reported previously, extended treatment with Femara reduced the risk of cancer recurrence.
  • Extended treatment with Femara also improved overall survival. Different statistical models provided somewhat different estimates of the extent of the benefit (one showed a 24% reduction in risk of death and the other showed a 39% reduction in risk of death), but both models showed a benefit.

The challenge of accounting for study participants who switched treatment groups introduced some uncertainty into these results, and they cannot be considered definitive. The results suggest, however, that for postmenopausal women who complete five years of tamoxifen, additional hormonal therapy with Femara may reduce the risk of breast cancer recurrence and improve overall survival.

Reference: Jin H, Tu D, Zhao N, Shepherd LE, Goss PE. Longer-term outcomes of letrozole versus placebo after 5 years of tamoxifen in the NCIC CTG MA.17 Trial: analyses adjusting for treatment cross-over. Journal of Clinical Oncology. Early online publication October 31, 2011.

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