TOPLINE:

Among over 76,000 women who received external beam radiation therapy (EBRT) for breast cancer between 2002 and 2017, those with left-sided disease had only slightly higher rates of heart failure and ischemic heart disease over 15 years than women treated for right-sided cancer. Their risk for a first-time hospitalization for cardiovascular disease was no higher.

METHODOLOGY:

• Women who received EBRT for left-sided breast cancer in the 1970s and ‘80s had higher rates of cardiovascular disease mortality than women treated for right-sided breast cancer. Recent data suggest that modern photon-based radiotherapy has substantially reduced that excess risk, but studies have been small or had relatively short follow-up.
• Researchers conducted a population-based, retrospective cohort study using linked administrative health databases in Ontario, Canada, to identify women who received EBRT for unilateral breast cancer between 2002 and 2017.
• A total of 76,586 women (mean age, 59 years) were included and followed up for a median of 11 years. Roughly half had been treated for left-sided disease.
• The primary outcome was hospitalization for cardiovascular disease, whereas secondary outcomes included all-cause mortality and new diagnoses of ischemic heart disease, heart failure, and atrial fibrillation. Cumulative incidence functions estimated the 15-year risk for outcomes accounting for the competing risk for death.

TAKEAWAY:

• The 15-year cumulative incidence of first cardiovascular disease hospitalization did not differ between women treated for left-sided or right-sided breast cancer (13.8% vs 13.5%, respectively; P = .43). Similarly, all-cause mortality rates were 26.1% and 26.0%, respectively.
• Among women without preexisting cardiovascular disease, new diagnoses of heart failure were slightly more frequent after left-sided vs right-sided EBRT (10.2% vs 9.6%; P = .01), as were new diagnoses of ischemic heart disease (13.6% vs 12.8%; P = .03).
• The rate of cardiovascular disease hospitalizations including recurrent events was modestly higher for women treated for left-sided vs right-sided disease (1.72 vs 1.63 per 100 person-years; P = .006), corresponding to a hazard ratio of 1.05 (P = .04).
• Among women younger than 50 years, left-sided tumor laterality was associated with increased risk for cardiovascular disease at 15 years (4.8% vs 3.9%; P = .02). However, no significant difference by laterality was noted among women 50 years or older.

IN PRACTICE:

“In this cohort study of women treated with EBRT for breast cancer in the past two decades, left-sided breast cancer radiation therapy was associated with minimal increases in long-term cardiovascular risk,” the study authors wrote. “These findings suggest that contemporary photon-based EBRT techniques have substantially reduced the cardiovascular risk historically associated with left-sided breast cancer radiation therapy.”

SOURCE:

The study, led by Erika Nakajima, MD, of Women’s College Hospital, Toronto, Ontario, was published online in JAMA Network Open.

LIMITATIONS:

Confounding cannot be ruled out despite the random nature of tumor laterality and lack of differences in baseline characteristics between the study groups. Administrative data lacked details such as radiation doses to the heart and treatment plans. The researchers were unable to differentiate between patients who received partial breast vs whole-breast radiotherapy or to study subclinical or imaging-based cardiac injury.

DISCLOSURES:

This study received support from the Heart and Stroke Association of Canada, the Canadian Institutes of Health Research, the University of Toronto, and ICES (formerly the Institute for Clinical Evaluative Sciences). Two authors disclosed receiving personal fees from various pharmaceutical companies outside the submitted work. Additional disclosures are noted in the original article.

This article was created using several editorial tools, including AI, as part of the process. Human editors reviewed this content before publication.