TUESDAY, March 22 (HealthDay News) -- Taking the breast cancer drug tamoxifen for the recommended five years protects women from breast cancer recurrence better than a two-year course of the drug and it also shields some women from cardiovascular disease, new research finds.

The cancer protection and heart-disease risk reduction were noted 15 years after starting treatment, according to the study published online March 21 in the Journal of Clinical Oncology.

The findings may surprise many women on the medication, said Allan Hackshaw, deputy director of Cancer Research and the University College London Cancer Trials Center. "I think many women don't realize the benefits [reduced cancer recurrence] last a long time if they can complete the five-year course, and particularly also the CV [cardiovascular] disease benefit," he said.

Hackshaw and his colleagues studied follow-up data for 3,449 participants in the Cancer Research UK "Over 50s" trial comparing tamoxifen use of five years and two years by women with early beast cancer. The women were between 50 and 81 at the start.

During the initial study period, 1987 to 1997, the women took 20 milligrams of tamoxifen a day for two years. After that, they were assigned randomly to stop taking the drug or to continue taking tamoxifen for three more years, if they were recurrence-free.

The researchers then tracked cancer recurrences, new tumors, death and cardiovascular events through April 2010.

There were 1,103 recurrences, 755 deaths from breast cancer, 621 cardiovascular events and 236 deaths from cardiovascular events. They found that 15 years after the women first began taking tamoxifen, for every 100 who took it for five years, nearly six fewer women suffered a recurrence compared to those on the two-year regimen.

The longer treatment reduced the risk of breast cancer developing in the opposite breast by 30 percent, the researchers found.

The effect on heart disease among women 50 to 59 years old was even stronger -- a 35 percent reduction in cardiovascular events and a 59 percent reduction in deaths from cardiovascular problems.

However, among older women the heart effect was much smaller and not statistically significant.

Tamoxifen, used for 30 years to treat breast cancer, inhibits the ability of estrogen-receptor positive cancers (the majority of breast cancers) to grow by disrupting estrogen activity.

It's not clear how the drug protects against heart disease, Hackshaw said. "But there is evidence that tamoxifen reduces lipid levels [for example, cholesterol], which we know in turn reduces cardiovascular risk," he explained.

It's possible that the protective effect declined in older women because damage to the arteries had already occurred, he speculated.

The new research is a timely reminder about the benefits of tamoxifen, said Dr. Joanne Mortimer, vice chair of medical oncology at the City of Hope Comprehensive Cancer Center, Duarte, Calif., and director of its women's cancers program.

Although many doctors prescribe medications known as aromatase inhibitors for breast cancer instead of tamoxifen, Mortimer said tamoxifen is still widely prescribed.

"Maybe for those who have problems with an aromatase inhibitor, they would be comforted by the fact that tamoxifen is an alternative and has a favorable effect on normal tissues, like bone and heart muscles," Mortimer said.

While not discounting the effectiveness of aromatase inhibitors, Hackshaw said tamoxifen is much less expensive.

A month's supply of 20-milligram tablets, the dose used in the Hackshaw study, is about $100. Brand-name versions of aromatase inhibitors can cost more than $500 for 30 pills, although cheaper generic versions are also available.

In an editorial accompanying the study, Dr. Kathleen Pritchard, of Sunnybrook Odette Cancer Center in Toronto, said the findings about heart protection should be regarded with ''some caution,'' although the finding is of interest.

Some research has found cardiovascular deaths higher in women on aromatase inhibitors than tamoxifen, she writes, although not all studies of tamoxifen have found the cardiovascular protection. So, still more research is needed, she said.

More information

To learn more about tamoxifen, visit the National Cancer Institute.

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