How likely are women with hormone receptor positive breast cancer to benefit from additional exemestane or tamoxifen?

This study looked at the benefit of additional hormone therapy in premenopausal women with hormone receptor-positive HER2 negative (HR+ HER2-) early breast cancer. They found that patients at higher risk of cancer returning showed greatest benefit from exemestane (Aromasin) plus ovarian function suppression (OFS).

HR+ HER2- breast cancer is often treated with chemotherapy and/or OFS (medications such as Trelstar, or surgical removal of the ovaries). Tamoxifen (Nolvadex) is a standard additional treatment for women with HR+ breast cancer. It prevents the hormone estrogen from triggering tumor growth. Recent studies have shown that treatment with exemestane plus OFS is better at preventing recurrence than tamoxifen plus OFS or tamoxifen alone.

Exemestane, a drug which prevents estrogen production, can have serious side effects. It is important to ensure patients are likely to benefit from the treatment. It is unclear if patients at low, medium and high risk of cancer returning all experience the same benefit from exemestane.

4,891 premenopausal (before menopause) women with HR+ HER2- early breast cancer were included in this study. Patients were graded based on their risk of breast cancer returning (based on factors such as tumor size, lymph node involvement, and the presence of certain proteins).

Patients at low risk, initially treated with tamoxifen alone, showed no improvement with additional exemestane plus OFS.

Patients at high risk, initially treated with OFS, were 10% less likely to have cancer recurrence with additional exemestane compared to additional tamoxifen.

Patients receiving chemotherapy and OFS were also less likely to see cancer return with additional exemestane compared to additional tamoxifen. Those at highest risk showed greatest benefit.

In patients treated with chemotherapy and tamoxifen, additional OFS decreased the likelihood of cancer returning compared to tamoxifen alone. The greatest decrease was seen in those at highest risk. 

This study concluded that exemestane plus OFS decreases the likelihood of breast cancer returning compared with tamoxifen plus OFS or tamoxifen alone. The greatest decrease is seen in patients most at risk. Side effects of exemestane should be weighed up against the likelihood of treatment to impact recurrence.