Women who undergo breast cancer radiotherapy do not face an increased risk for subsequent heart conduction problems requiring a pacemaker as a result of their treatment, according to new research reported here at the European Society for Radiotherapy and Oncology (ESTRO) 3rd Forum.

“If a woman receives a pacemaker after breast cancer we can assure her it was not due to her therapy,” said study investigator Jens Christian Rehammar, MD, from Odense University Hospital in Denmark.

“Our study is quite unique, as there are no corresponding large studies in breast cancer patients only — previous studies are often mixed with patients with Hodgkin’s lymphoma,” he told Medscape Medical News.
The findings are good news considering recent evidence that an increase in other types of cardiac problems is associated with breast radiotherapy, Dr Rehammar said. He was referring to a 2013 study that found that for every additional gray of radiation to the breast there is 7.4% increase in major coronary events (P < .001) including myocardial infarction, the need for coronary revascularization, and dying from ischemic heart disease ( N Engl J Med. 2013 Mar 14;368(11):987-998).

Analysis of Danish Data

Dr Rehammar’s study merged data from the Danish Breast Cancer Collaborative Group with data from the Danish Pacemaker and ICD Registry to compare women who did and did not receive breast radiotherapy and their likelihood of needing a subsequent pacemaker.

A total of 44,704 women were included in the analysis.

The study found that among 18,308 breast cancer patients who received radiotherapy, 179 (0.98%) received a pacemaker, 90 of whom had been treated for left-sided and 89 for right-sided breast cancers.

For comparison, 1.54% of the nonradiotherapy patients received a pacemaker.

After adjusting for year of treatment, age, and time since breast cancer diagnosis, the risk for cardiac conduction problems requiring a pacemaker was not significantly different between the two groups (relative risk, 1.06; P = .71), he said.
Asked by Medscape Medical News to comment on the findings, Ben Smith, MD, assistant professor of radiation oncology at The University of Texas MD Anderson Cancer Center in Houston, said, “Conduction problems have not really been studied before in breast patients, to my knowledge. I would have predicted this would be a negative study, but it is nice to have data to confirm that.”

Dr Smith, who wrote a recent review of cardiac effects of breast radiotherapy, added, “This study provides reassurance that the typical doses of radiation received by the heart during this era in Denmark did not produce clinically severe damage to the heart’s conduction system. When coupled with prior studies, this body of work suggests that the primary mechanism for cardiac damage following breast cancer radiation is vascular in origin. The conduction apparatus in the heart is fair away from the breast, whereas the blood vessels that feed the heart are closer to the breast.”