Jennifer Bernier is just 18 and already has battled two major illnesses. When she was 9, she got cancer. Then, at 14, she developed heart disease.

It may seem profoundly unfair, but she is one of many childhood cancer survivors who face a second life-threatening condition brought on by treatment of the first.

In the largest study of its kind, University of Minnesota researchers found that children who survive cancer are five to 10 times more likely to develop heart disease than their healthy siblings.

Scientists have long known that cancer treatment can damage the heart. But the study, released Thursday, found that survivors of eight childhood cancers suffer from heart attacks, clogged arteries and other heart problems at much younger ages than their peers.

The risk of heart disease continues to rise as long as 30 years after the cancer diagnosis.

"I say this to survivors frequently: It doesn't mean you're all going to get this, even though the risk sounds extremely large," said Dr. Daniel Mulrooney, a children's cancer specialist at the University of Minnesota, who led the study. It is one of several studies that will be featured at the upcoming annual meeting of the American Society of Clinical Oncology.

In all, about 4 percent of the cancer survivors developed congestive heart failure, the study found. But the study of more than 14,000 survivors suggests they need to be monitored closely for signs of heart problems as early as their teens and 20s.

For Jennifer, that is simply a part of life now. Next week, she is graduating from high school in Ellsworth, Wis. She plans to study nursing and eventually work with childhood cancer.

"Sometimes I can't run as fast because of my heart condition," said the teenager, who played volleyball, softball and basketball in school. Today, she takes medicine to help her heart pump normally, but other than that, she said, "I'm pretty normal."

Jennifer learned she had cancer on her ninth birthday, in November 1998. The cancer, known as Ewing's sarcoma, was in her backbone and couldn't be removed. So she spent nearly a year getting chemotherapy at the University of Minnesota, followed by radiation at a California hospital. She lost her hair and missed most of third grade. But after that, "everything pretty much went back to normal." Although the tumor never completely went away, she said, it has remained inactive ever since. "Pretty much, I'm cured."

At checkups, her doctors at the university routinely monitored her heart for any sign of damage from her treatment. When she was 14, they found it: Her heart was pumping abnormally, a condition that can lead to congestive heart failure.

"Of course, I was upset that I had it," said Jennifer. But after all she had been through, "I didn't really see it as that big of a problem. I just learned that I'd have to live it with it, just like I've lived with everything else."

Mulrooney said heart damage can be caused by radiation or chemotherapy, especially by a group of drugs called anthracyclines that are still widely used.

Those drugs, he noted, are "very effective -- you can point to them and say they've contributed greatly to the improvement in survival we've realized in childhood cancer." Today, about 80 percent of patients survive childhood cancer. "So we don't want to abandon effective agents, but we need to find better ways to use them to prevent long-term effects."

Other studies also have found that cancer survivors have higher rates of infertility, depression and heart diseases. But this is one of the largest such groups ever studied, including survivors of leukemia, lymphoma, kidney tumors, bone cancers and other tumors.

Mulrooney and his colleagues used a registry of childhood cancer survivors, started at the University of Minnesota, to study children and teenagers who were diagnosed with cancer between 1970 and 1986. The researchers compared more than 14,000 former patients to 3,900 of their siblings who never had cancer.

Roughly 20 years after diagnosis, the cancer survivors had:

• 10 times the risk of hardening of the arteries;

• Nearly six times the risk of congestive heart failure.

• Five times the risk of heart attack.

• Five to six times the risk of disorders of the heart valve or membrane surrounding the heart.

Mulrooney said there are about 270,000 survivors of childhood cancer in the country and they need to be monitored for heart disease. The study, he said, suggests that the screening "should begin early and be lifelong."

Maura Lerner • 612-673-7384