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.
Giordano cautions that death from ischemic heart disease may not present until 15 years post-treatment, therefore longer follow-up will need to be continued to confirm that the risk to patients has been completely eliminated.
According to the study, in 2002 approximately 42 percent of breast cancer patients received adjuvant radiation therapy after surgery, a treatment combination which dramatically decreases the risk of disease recurrence while increasing survival. The risk of cardiac complications is a great concern to many patients receiving radiation therapy, says Thomas A. Buchholz, M.D., professor in M. D. Anderson's Department of Radiation Oncology.
"Heart complications associated with radiation treatment really became appreciated in the 1980s, leading to improvements in technique and delivery," says Buchholz. "This study highlights the progress made more than 10 years ago. Receiving radiation will only become safer and safer for patients as we move forward, with newer radiation techniques allowing treatment to exclusively target tumors, while sparing healthy tissue."
Giordano believes that this study will encourage patients in need of radiation therapy for breast cancer to proceed with treatment without fear.
"A substantial number of women, especially those who are older, don't get radiation when they should - for example after a lumpectomy. We really don't know why they don't get radiation, but we have to theorize that maybe it's due to concerns over toxicity," Giordano says. "This study should reassure all patients that radiation has become safer and there is little, if any, risk of future ischemic heart disease due to having received radiation."