The finding suggests doctors need to monitor these patients earlier, and manage their risk factors for heart diseases while they are still young.
"Research has shown childhood cancer survivors face heart and other health problems decades after treatment," study author Donald Dengel, a kinesiology professor at the University of Minnesota in Minneapolis, said in an American Heart Association news release. "But researchers had not, until now, looked at the heart health effects of childhood cancer treatment while survivors are still children."
The researchers assessed artery stiffness, thickness and function in more than 300 boys and girls, ages 9 to 18, who had survived at least five years since their diagnosis of leukemia or cancerous tumors. Arteries are blood vessels that take blood away from the heart.
These patients were compared with more than 200 siblings who did not have cancer.
The childhood cancer survivors were more likely to have a decline in arterial function that indicated premature heart disease, according to the study, scheduled for presentation Sunday at the annual meeting of the American Heart Association in Dallas.
The researchers also found that childhood leukemia survivors had a 9 percent decrease in arterial health after completing chemotherapy, compared to the children without cancer.
"Given this increased risk, children who survive cancer should make lifestyle changes to lower their cardiovascular risk," Dengel said. "Health care providers who are managing chemotherapy-treated childhood cancer survivors need to monitor cardiovascular risk factors immediately following the completion of their patients' cancer therapy."
The children in the study were predominantly white, so the findings might not apply to other racial and ethnic groups. In addition, the researchers were unable to link heart changes to any specific chemotherapy agent.
The five-year survival rate for childhood cancers in the United States increased from about 58 percent in 1975-77 to about 83 percent in 2003-09.
Data and conclusions presented at meetings are typically considered preliminary until published in a peer-reviewed medical journal.
The U.S. National Cancer Institute talks about late effects of childhood cancer treatment.