FRIDAY, Oct. 10, 2008 (HealthDay News) -- Tamoxifen, the drug used for more than 30 years to treat breast cancer, reduces the risk of osteoporosis-related fractures, a new study shows.
"The effects are almost instantaneous," said study author Dr. Andrew Cooke, head of radiation oncology at CancerCare Manitoba in Winnipeg, Manitoba, Canada.
However, he added, "The fracture risk goes right back up once you stop it. The good news is, it reduces fracture risk when you are on it. Once you stop, you are not protected."
The findings are published in the Nov. 10 issue of the Journal of Clinical Oncology.
Previous studies have found that women on tamoxifen have increased bone mineral density. And patients taking tamoxifen, compared to another class of breast cancer drugs, aromatase inhibitors, have a reduced risk of fracture.
For the new study, Cooke and his colleagues compared more than 11,000 women aged 50 and older who had osteoporotic fractures of the spine, wrist or hip with more than 33,000 control patients who did not have fractures. All the women were matched for age, ethnicity and other health problems. The researchers also noted whether the women were currently taking tamoxifen, had done so in the past or had never used the drug.
Current use of tamoxifen reduced osetoporosis-related fracture risk overall by 32 percent and reduced hip fractures by 53 percent.
"It obviously helps," said Cooke.
But, he added, the study did not find that women who had taken tamoxifen in the recent past were protected against fractures.
Breast cancer patients are known to be at increased risk for osteoporosis and all types of fractures because of the effects of chemotherapy and other drugs used to treat the disease.
Tamoxifen is taken orally as a tablet and interferes with the activity of the female hormone estrogen, which can promote cancer development in the breast. The drug blocks the ability of a tumor to use estrogen, preventing its growth. It is often used to treat patients with early stage breast cancer and those whose cancer has spread.
Aromatase inhibitors are also used in breast cancer treatment. They work by lowering the amount of estrogen in the body but have been associated with decreased bone density, upping fracture risk.
The new study adds to information about tamoxifen's effects, said Dr. Christy Russell, associate professor of medicine at the University of Southern California Keck School of Medicine, and chair of the American Cancer Society's Breast Cancer Advisory Group.
"We have known from large breast cancer trials comparing tamoxifen to aromatase inhibitors that the fracture rates were higher in [those who got] aromatase inhibitors than tamoxifen," she said. "But we had not known whether the fracture rate on tamoxifen was lower than in women not being given tamoxifen and given nothing. This study gives that information."
Russell said the study results may cause some doctors to rethink when they prescribe tamoxifen and aromatase inhibitors. Currently, some doctors use aromatase inhibitors alone for postmenopausal breast cancer patients, while others use tamoxifen then aromatase inhibitors. The new findings may lend weight to the value of giving tamoxifen first, she said.
Dr. Len Lichtenfeld, the American Cancer Society's deputy chief medical officer, said the take-home message from the new study was this: "If you switch from tamoxifen to aromatase inhibitors, or if you stop tamoxifen, you must be aware your osteoporosis risk may increase."
Women should then ask their doctor how best to protect their bone health, he said.
To learn more about tamoxifen, visit the National Cancer Institute.