Modern radiation therapy for early breast cancer seems to be much less toxic to the heart than older radiation regimens, according to a University of Michigan-Ann Arbor study.

A “critical component” of therapy, radiation therapy reduces the risk of breast cancer recurrence and improves survival after breast-conserving surgery in women with early breast cancer, the study team notes in the journal Cancer.

“However, older techniques of radiation therapy resulted in substantial radiation doses to the heart, particularly in patients with left-sided breast cancer,” UM oncologist and first author Dr. Reshma Jagsi told Reuters Health. These regimens were found to raise the risk of heart disease. But the impact on the heart of more modern radiation regimens is less well known.

“We wished to examine whether women treated with radiation after breast-conserving surgery for early-stage breast cancer at our institution in the 1980s and 1990s had an increased risk of coronary artery disease,” Jagsi said.

The team found, based on the records of more than 800 women, that the rates of heart attack and heart disease that required treatment were very low; in fact, the rates were significantly lower than the rates that would normally be expected in women without breast cancer.

“We did find a slight increase in the risk of heart attacks in patients treated to the left side of the chest compared to those treated to the right side,” Jagsi said. “However, the absolute risk was extremely low.”

Twelve women (1.4 percent) suffered at least one heart attack and 20 (2.4 percent) had at least one heart attack or episode of coronary artery disease requiring treatment after an average follow-up time of 6.8 years.

The 10-year rate of heart attack was 1.2 percent and the rate of heart attack or heart disease requiring treatment was 2.7 percent. The average interval from radiation treatment to a heart disease event was 3.7 years. Heart attacks and other cardiac-related events after radiation therapy occurred most often in older smokers with diabetes.

Despite the very low risk, “our study provides evidence to support the exploration of more sophisticated techniques of radiation treatment that reduce the radiation dose received by the heart,” Jagsi told Reuters Health.

“Our findings,” the researcher emphasized, “do not in any way suggest that patients treated with breast-conserving therapy should consider omitting radiation, as radiation is critical for reducing the much more substantial risks of recurrence and death from breast cancer in these patients.”

SOURCE: Cancer 2007.