In the largest and most comprehensive prospective study of its kind, researchers at The University of Texas M. D. Anderson Cancer Center have concluded that the risk of ischemic heart disease and, ultimately, cardiac death following radiation treatment for breast cancer has steadily declined over the last quarter century, according to a new study published in the March 16 issue of the Journal of the National Cancer Institute.
This study offers scientific evidence to what was long thought to be true but never proven: that improvements in radiation techniques and delivery have greatly impacted radiation-associated cardiac mortality.
"For a while now, physicians have been telling women that receiving radiation for breast cancer is so much safer today than it was before. People believed it, but there really was very little scientific evidence or studies examining the relationship between advancements in radiation therapy to ischemic heart disease," says Sharon Giordano, M.D., the study's lead author and an assistant professor in M. D. Anderson's Department of Breast Medical Oncology. "Before now, there were no studies that looked at the effects of radiation to the heart over time. Most previous analyses had involved women who had been treated in the 1950s, 1960s and 1970s, decades not considered in the era of modern medicine.
"Comparing women with breast cancer on the left side where the heart is located (therefore, more radiation is delivered to the heart) versus those with disease on the right side gave us a perfect study to examine radiation-induced toxicity to the heart and cardiac mortality," she continues.
Giordano and her colleagues used information from the National Cancer Institute SEER database (Surveillance, Epidemiology, and End Results), the authoritative source of information on cancer incidence and survival in the United States. The researchers analyzed SEER data from 1973 to 1989 on 27,283 women - 13,998 had left-sided breast cancer, 13,285 had right-sided breast cancer. Patients were stratified into three cohorts by date diagnosed - 1973 to 1979, 1980 to 1984 and 1985 to 1989. Mortality from ischemic heart disease, heart problems caused by narrowing of the arteries, was compared in the three cohorts.
Of the women studied that were diagnosed in the 1970s, those with tumors on the left side had an increased ischemic heart disease mortality after 15 years (13.1 percent) compared to patients with tumors on the right side (10.2 percent).
However, of the women diagnosed from 1980-1984 and from 1985 to 1989, there was no such difference in cardiac mortality. The researchers concluded that each year after 1979, the risk of death from ischemic heart disease declined by six percent annually in women with left sided breast cancer compared to those with disease on their right side.