Adding bevacizumab to letrozole treatment in hormone receptor-positive metastatic breast cancer – A good idea?

This study looked at the effect of adding bevacizumab (Avastin) to letrozole (Femara) treatment in patients with hormone receptor-positive (HR+) metastatic (spread to other areas) breast cancer. They found that bevacizumab treatment prolonged the amount of time before patients experienced worsening of their condition. However, it did not improve survival and patients were more likely to experience serious side effects. 

HR+ metastatic breast cancer depends on hormones such as estrogen or progesterone for growth.  A main treatment option for HR+ breast cancer is blocking the hormones, which can decrease cancer growth. Letrozole is an example of a treatment that reduces the production of estrogen.

Tumors also depend on the formation of new blood vessels. Without a blood supply, tumors cannot grow. Bevacizumab is a treatment that blocks the growth of new blood vessels. It is not clear whether bevacizumab would be effective in combination with letrozole.

343 women with HR+ metastatic breast cancer were included in this study. Patients were randomly split into two groups. One group received letrozole plus bevacizumab. The other group received letrozole plus a placebo (substance which has no effect on the body).

Patients receiving bevacizumab were 25% less likely to have experienced worsening of their condition during the timeframe of the study. Bevacizumab was associated with an additional 4.6 months without disease progression compared to letrozole alone. There was no significant difference in survival rates between the two groups.

Patients taking bevacizumab were more likely to experience serious side effects. Serious high blood pressure occurred in 24%, compared to 2% of patients treated only with letrozole. Kidney damage occurred in 11% of those treated with bevacizumab, and 0% of those treated with letrozole alone. 

This study concluded that addition of bevacizumab to standard letrozole treatment increases the time a patient may have without worsening of their condition. However, it does not improve survival and has is associated with increased risk of serious side effects.

This study was part funded by the pharmaceutical companies Gentech and Novartis.