Oct. 21, 2011 -- Older women with early breast cancers are more likely to live longer and less likely to have the cancer come back when they take the drug Femara (letrozole) instead of tamoxifen, a long-term follow-up study shows.
At an average follow-up of more than eight years, postmenopausal women who took Femara for five years after surgery were 20% less likely to have their breast cancer return and 21% less likely to die from their breast cancer compared to postmenopausal women who took tamoxifen.
Femara is an aromatase inhibitor. Aromatase inhibitors are now generally considered the hormonal treatment first used by most postmenopausal early breast cancer patients whose tumors are fueled by estrogen, but not all women can take the drugs.
The drugs work by blocking the production of aromatase, which turns the hormone androgen into estrogen in the body. But because they don't stop the ovaries from making estrogen, they are not used to treat breast cancer patients who are still ovulating.
Breast Cancer Survivors
There are more than 2.6 million breast cancer survivors living in the U.S., according to the American Cancer Society.
About 230,000 new breast cancers are expected to be diagnosed in the U.S. this year and about 40,000 women will die of the disease.
The new updated analysis from the previously published Breast International Group (BIG) study adds to the evidence showing that aromatase inhibitors may be a more effective treatment than tamoxifen for postmenopausal women with estrogen-dependent tumors.
The study included just over 8,000 postmenopausal women living in 27 countries who had undergone surgery for cancers that had not spread beyond the breasts and lymph nodes.
One group of patients took either tamoxifen or Femara for five years. Another took tamoxifen for two years followed by three years of Femara or two years of Femara followed by three years of tamoxifen.
The study was originally funded by Femara manufacturer Novartis. But the drugmaker is no longer funding the continuing patient analysis, researcher Meredith M. Regan, ScD, tells WebMD.
With patient follow-up averaging more than eight years, daily treatment with Femara decreased relapse risk and death from breast cancer by about one-fifth, compared to treatment with tamoxifen.
Treating Breast Cancer
Neither tamoxifen followed by Femara nor Femara followed by tamoxifen were more effective treatments than Femara alone.
The updated analysis appears in the Oct. 21 issue of The Lancet.
"The hope was that sequential treatment with one drug followed by another would be more beneficial than the single drug, but that is not what the study found," says Stephanie Bernik, MD, who is chief of surgical oncology at Lenox Hill Hospital in New York City.
In addition to Femara, two other aromatase inhibitors are widely used in the treatment of postmenopausal women with estrogen-receptor positive breast cancers: AstraZeneca's Arimidex (anastrozole) and Pfizer's Aromasin (exemestane).
"It appears that the class of drugs offers better outcomes, but there is still a role for tamoxifen," she says. "Some patients can't tolerate aromatase inhibitors."
Tamoxifen Side Effects
Tamoxifen is still widely used in the treatment of younger breast cancer patients, and it is the only drug approved to treat ductal carcinoma in situ (DCIS) -- early breast cancer that has not spread beyond the milk ducts.
Side effects of tamoxifen can include blood clots and an increased risk for endometrial cancer, while potential side effects with aromatase inhibitors include bone loss, an increased risk for heart disease, and joint pain.
Breast cancer specialist Jane Carleton, MD, of the North Shore-LIJ Health System Monter Cancer Center in New York, says between 30% and 50% of patients who take an aromatase inhibitor experience joint pain.
"This is a very common side effect," she tells WebMD.