Many cancer treatments have a dark side — they can damage the heart. New research suggests this risk might be lowered in women with breast tumors if they take a heart drug as a preventive measure during their cancer care.

If confirmed in wider testing, this could improve care for thousands of breast cancer patients in the U.S. alone each year, plus other women and some men who also get these treatments for other types of cancer.

As it stands now, cancer patients are referred to cardiologists after certain cancer drugs or radiation treatments have already weakened their hearts. Special clinics are springing up in hospitals to take care of the growing number of cancer survivors with this problem.

"If you wait until the disease has occurred, it may be too late" to do much good, said Dr. Javid Moslehi, who heads one such specialty clinic at Vanderbilt University. "We in the cardiology community have to do a better job of preventing cardiac disease rather than jumping in" after damage has occurred.

He had no role in the new study, which was done in Norway. Results were discussed Wednesday at an American Heart Association conference in Orlando.

Radiation treatments can harm arteries, making them prone to harden and clog and cause a heart attack. It also can cause valve or rhythm troubles. Certain cancer drugs, such as Herceptin and doxorubicin, sold as Adriamycin and other brands, can hurt the heart's ability to pump, and lead to heart failure.

"We give poison with a purpose," because it fights cancer, but heart problems can be "one of the dark sides of that," said Dr. Ann Partridge, a breast cancer specialist at the Dana-Farber Cancer Institute in Boston.

One of her patients, Christine Ells, 36, a teacher in the Boston suburb of Quincy, developed a heart rhythm problem from several drugs she was given to treat the breast cancer she was diagnosed with at age 27.

"The risks of these drugs are crazy," she said, but "it was more important to cure my cancer."

The new study aimed to prevent cardiac side effects. Led by Dr. Geeta Gulati of Akershus University Hospital in Lorenskog, Norway, it involved 120 women with early-stage breast cancer and tested two drugs long used to treat high blood pressure and heart failure — candesartan and metoprolol. The drugs are available as generics and cost less than a dollar a day.

Women were given one or both drugs or dummy pills, and their hearts' pumping capacity was assessed at various time points with MRI scans.

Heart damage worsened in the group on dummy pills. Metoprolol did not prevent heart decline but candesartan did, although the benefit was small — an improvement of 2 percent to 3 percent in pumping strength compared to the placebo group.

"The major issue is, the effect was very modest," so whether that prevents heart failure from developing down the road is not known, said Dr. Bonnie Ky, a cardio-oncology specialist at the University of Pennsylvania.

It's also not known whether things get better or worse over time, or whether a different drug in the same class would work better.

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Still, it's a first.

As cancer patients are living longer, the risk of dying from heart problems actually exceeds that of cancer, so it's important to prevent damage, Ky said.

The University of South Florida has a federally funded study underway, testing drugs to prevent heart failure for women on Herceptin, that may help answer some questions.

Meanwhile, some doctors already are considering this tactic, especially in women taking drugs known to harm the heart or who already have some risk factors for heart problems.

"I get calls from the oncologists saying, 'she's at high risk, why don't we just start it?'" Dr. David Slosky, a cardiologist at Vanderbilt, said of preventive treatment.

"They're pretty benign," he said of the heart drugs the study tested. "The threshold, if somebody's got a high-risk cancer, will be pretty low" to use them preventively, he said.