For postmenopausal women with hormone-driven breast cancer, follow-on treatment with Femara is more effective in preventing recurrence of cancer than is tamoxifen, a study shows.

Femara is in the class of drugs called aromatase inhibitors, which suppress estrogen production, and is known generically as letrozole.

“Letrozole gives a 19 percent additional risk reduction against a cancer event or death above and beyond that what can be achieved with tamoxifen,” said Dr. Beat J. Thurlimann.

Thurlimann, from University of Basel in Switzerland, presented the study findings Friday on opening day of the annual meeting of the American Society of Clinical Oncology.

In the study, investigators documented breast cancer recurrence in more than 8,000 postmenopausal women taking either tamoxifen for 5 years, letrozole for 5 years, tamoxifen for 2 years followed by letrozole for 3 years, or letrozole for 2 years followed by tamoxifen for 3 years.

Letrozole not only lowered the risk of breast cancer recurrence by 19 percent over tamoxifen, it also lowered the risk of distant spread of the disease - metastases - by 27 percent compared with tamoxifen.

“The 27 percent risk reduction is important because distant metastases will ultimately lead to death,” Thurlimann said. “Thus, better protection here is expected to translate to improved overall survival.”

Both letrozole and tamoxifen were generally well tolerated with a low rate of serious side effects.

Nonetheless, the two drugs do have different kinds of side effects. For example, blood clotting is more likely with tamoxifen while more bone fractures occur on Femara treatment.

These differences this should be considered in deciding which drug is best for a particular woman, Thurlimann concluded.