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Breast cancer patients who double the length of time that they take acommon medication can sharply reduce their risk of death, according toa new study that's predicted to influence medical practice.

Thestudy involved an estrogen-blocking pill called tamoxifen, a standardtherapy for the roughly two-thirds of breast cancer patients whosetumors are sensitive to estrogen. Taking tamoxifen for five years afterdiagnosis reduces breast cancer mortality by about one-third.

Inthe new study, women with early tumors who took tamoxifen for 10 yearscut their risk of dying from breast cancer by another 29%, compared towomen who stopped after five years.

In absolute terms, 12% ofwomen on tamoxifen for 10 years died of breast cancer within five to 14years after diagnosis, compared to 15% of those who stopped at fiveyears.

Overall, women who take tamoxifen for a decade cut theirrisk of dying from breast cancer nearly in half, compared with those whodon't take it at all, says study co-author Richard Gray of theUniversity of Oxford in the United Kingdom.

That's significant,given that tamoxifen is used by hundreds of thousands of womenworldwide, says Gray, whose study was presented Wednesday at the annualSan Antonio Breast Cancer Symposium. Oxford funded the study, whichincluded more than 6,800 women from 36 countries, While tamoxifendelays tumor growth in some women, it appears to cure others, Gray says.

"This is a dream come true for women," says V. Craig Jordan, aresearcher who led tamoxifen's development, but who wasn't involved inthe new study. "It's very exciting."

Tamoxifen, which has beenused for decades, is far cheaper than most new chemotherapies andbiological drugs, which cost thousands of dollars a month. A genericversion costs about $100 a month in the USA, according to Susan G. Komenfor the Cure.

In the U.K., tamoxifen costs only $5 a month. InIndia, it's 2 cents a pill, says Jordan, scientific director atGeorgetown's Lombardi Comprehensive Cancer Center.

Jordan says the new findings will quickly change care for some patients.

Younger women with more aggressive tumors may want to extend theirtamoxifen use, says Jennifer Litton, an assistant professor at M.D.Anderson Cancer Center in Houston, who wasn't involved in the study.

Tamoxifen is the only hormonal option for women before menopause, Litton says.

Doctors may not want to change the care of older patients, however, shesays. That's because postmenopausal women have the option of tamoxifenor another class of hormonal therapies, called aromatase inhibitors, orAIs. These drugs are slightly more effective than tamoxifen, althoughthey don't work before menopause, Litton says.

Because the studydidn't include AIs, doctors can't say how whether tamoxifen wouldbenefit women who've taken them, Litton says. Other researchers areconducting trials comparing five versus 10 years of AIs, although theseresults won't be out for several years.

Gray noted that tamoxifenhas risks. In his study, doubling the length of treament also doubledthe risk of endometrial cancer, which affects the uterine lining, toabout 3%. However, because this cancer is very treatable, death rateswere low: 0.4% of those on tamoxifen for 10 years died of endometrialcancer, compared to 0.2% of those taking it for five years.

Doctors saw no increase in strokes, which has long been a concern with tamoxifen, Gray says.

Breast cancer survivors have mixed reactions to the results.

Some women will be glad to have another treament option, says breastcancer survivor Lillie Shockney, 59, administrative director of theJohns Hopkins Cancer Survivorhip Program in Baltimore.

"Patientsget very nervous when they stop any hormonal therapy, because they feellike now they aren't doing anything," says Shockney, 59. "Theopportunity to 'do something' might be appealing, despite the sideeffects."

Shockney says she'd like to see research on other waysto prevent recurrences, such as weight loss. "If someone lost 40 pounds,would that do as much as another five years on tamoxifen?" Shockneyasks.

Some patients may be reluctant to prolong their use of adrug that causes so many side effects, says Boston breast cancersurvivor Alicia Staley.

Studies show that only 80% of women taketamoxifen for five years, Litton says. Some switch to an AI, althoughthese drugs can also cause problems, such as joint pain andosteoporosis.

Staley say she tamoxifen gave her "many, many sideeffects," including severe hot flashes. "Dry eyes, joint pain, weightgain - you name it, I had it," she says.

After 2½ years, Staley and her doctor stopped the drug "to regain a measure of quality of life."

For Shockney, tamoxifen took a heavy toll on her marriage, causing dryness that made sex unbearably painful.

Patientsand their partners need to have honest talks with doctors about howextended treatment will affect their relationship, she says.

"Ifwe are going to look at giving women tamoxifen for 10 years, by golly,we better get the partners involved," Shockney says.

Yet Shockney says her husband of nearly 35 years would have wanted her to do everything possible to survive.

"If someone said to my husband, 'I know this has been a rough road foryou, and a big impact on your sex life, but if she stays on it anotherfive years. it could affect her survival,' he would have said, 'Please,please, take the pill.' "

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