Left-Side Breast Cancer EBRT Linked to Minimal Long-Term Cardiovascular Risk

By: Mary Ellen Schneider

From: cancertherapyadvisor.com

External beam radiation therapy (EBRT) for left-sided breast cancer has limited long-term cardiovascular risks, according to results published in JAMA Network Open.

The findings suggest that contemporary photon-based EBRT techniques that reduce mean radiation dose to the heart have resulted in lower cardiovascular risks than those historically associated with left-side breast cancer radiation treatment, the researchers wrote.

“These data may aid clinicians and patients when discussing the risks and benefits of EBRT, specifically in clinical settings where heart doses are expected to be low,” the researchers wrote.

In the population-based cohort study, researchers evaluated the long-term risk of cardiovascular disease (CVD) for women receiving photon-based EBRT for left- versus right-side breast cancer.

Researchers used linked administrative datasets on physician and hospital services, breast cancer diagnoses, surgeries, and radiation therapy for patients in Ontario, Canada. The datasets were used to create a cohort of women diagnosed with breast cancer who underwent photon-based EBRT from April 2002 through December 2017.

A total of 76,586 women were included in the analysis. Half had left-sided breast tumors, and the mean patient age in the cohort was 59 years.

During a median follow-up of 10.9 years, researchers found no significant difference in the 15-year incidence of first hospitalization for any CVD event between left- and right-sided tumors (13.8 % vs 13.5%; P =.43) . Tumor laterality was not significantly linked with the hazard of hospitalization for CVD even after adjusting for baseline covariates (hazard ratio [HR], 1.02; 95% CI, 0.98-1.06; P =.36).

There was also no difference in the 15-year incidence of coronary artery revascularization based on tumor laterality. The incidence was 2.2% for both left- and right-sided tumors (P =.97).

However, patients with left-sided tumors had a higher incidence of new diagnosis of heart failure at 15 years compared with patients with right-sided tumors (10.2% vs. 9.6%, P =.01). Similarly, patients with left-sided tumors also had an increased risk for a new diagnosis of ischemic heart disease at 15 years following radiation therapy (13.6% vs. 12.8%, P =.03).

When researchers examined cardiovascular outcomes per 100 person-years, they found an elevated rate of hospitalization for all CVD in patients with left-sided tumors (1.72 vs. 1.63 per 100 person-years; HR, 1.05; 95% CI, 1.00-1.11; P =.04).

Stratified analyses showed that both women younger than 50 years and women who received chemotherapy had an increased risk of CVD at 15 years with left-sided tumors.

“These findings provide population-level reassurance that modern radiation techniques have largely mitigated the excess long-term cardiovascular mortality and morbidity historically associated with left-sided [breast cancer] treatment for women with typical radiation exposure,” the researchers wrote.