Be aware Left sided radiation therapy and cardiac risk

[Lani]

Left-Sided Radiation for Breast Cancer Ups Heart Disease Risk

Lisa Nainggolan

August 17, 2006 — A new study shows that women with early-stage breast cancer who received radiation therapy to the left side of the chest were more likely to develop heart disease over the course of 2 decades than those who received right-sided radiation.

Eleanor E. R. Harris, MD, from the Moffitt Cancer Center and Research Institute in Tampa, Florida, and her team at the University of Pennsylvania — where she worked when conducting the research — report their findings online August 14 in the Journal of Clinical Oncology.

In an accompanying editorial, Abram Recht, MD, from the Harvard Medical School in Boston, Massachusetts, says the article by Dr. Harris and colleagues "is very important; it brings together long-term data on a relatively large number of fairly homogeneously treated patients with information on coexisting risk factors for coronary heart disease and determination of events gathered by review of individual medical records."

Hypertension Increases Risk of Radiation-Induced Heart Disease

Dr. Harris explained to Medscape that her study examined the use of contemporary radiation techniques for early breast cancer employed in the United States from the late 1970s onward, which were designed to minimize exposure to the heart, as previous research on this subject has involved outdated radiation techniques.

They set out to see whether 961 consecutive patients presenting from 1977 to 1994 had a higher rate of coronary artery disease (CAD) and cardiac death following left-sided radiation compared with right-sided radiation and whether any baseline cardiac risk factors interacted with left-sided radiation to increase the risk of CAD.

In the second decade after treatment, there was a higher rate of cardiac deaths in left-sided patients, with a cumulative risk of 6.4% for left-sided patients compared with 3.6% for right-sided patients at 20 years. There were also statistically higher rates of chest pain, CAD, and myocardial infarction (MI) diagnosed in left-sided patients (P < .002). Of the baseline cardiac risk factors, only hypertension was associated with a higher risk of CAD in left-sided patients.

Anthracyclines and Trastuzumab Were Not Involved

A limitation of the study, however, was that patients did not generally receive anthracyclines, which are now standard therapy for many breast cancer patients, nor did they get trastuzumab (Herceptin, Genentech), which is given to around 30% of patients. Both of these drug regimens can also cause cardiotoxicity, although Dr. Harris stressed that the mechanisms are different for all 3 treatment modalities.

"Radiation affects the coronary arteries and causes CAD and MI, whereas anthracyclines cause heart failure, and we think Herceptin interacts with a cardiac antibody. However, we definitely need more data on how these interact to affect the heart. The next study needs to be done with really state-of-the art chemotherapy," she explained.

"But the take-home message for now is that if you’ve had radiation to the left side of the chest, you have an increased risk of CAD, particularly if you are also hypertensive."

Such patients should make sure they have regular checks of blood pressure, cholesterol, and other risk factors, she noted, although she admitted that she does not know how often patients should get checked but is looking at this issue in a follow-up study.

"People often forget that they have had breast cancer and treatment as the years go on, but I can’t stress strongly enough that surveillance needs to be long-term," she concluded.

In his editorial, Dr. Recht says there is just one discrepancy with a previous study, in which smoking was found to be a risk factor for subsequent development of coronary heart disease following left-sided irradiation, but not hypertension. "I strongly encourage patients to vigorously treat their hypertension and hyperlipidemia — and, for God’s sake, stop smoking!" he says.

Newer Techniques Under Investigation

Dr. Harris explained that there is still much work to be done and there are many areas of debate among radiation oncologists as to how best to reduce the risk of radiation-induced heart disease.

Newer techniques under investigation to further reduce the exposure of the heart include accelerated partial-breast irradiation and intensity-modulated radiation therapy, she said.

"We are endeavoring to make sure there is no heart in the radiation field, but in some women, their anatomy makes this impossible," she concluded.

J Clin Oncol. Published online August 14, 2006.