Cardiac Surveillance in Breast Cancer Survivors Who Received IMC Radiation?

A large Dutch study found that internal mammary chain (IMC) radiation therapy for breast cancer is associated with increased cardiac toxicity, in particular when paired with anthracycline-based chemotherapy. Though this highlights the need for vigilance with regard to this potential side effect, that type of radiation is no longer commonly used in clinical practice.

“Since the 1970s, thousands of women in the Netherlands have been treated with IMC irradiation using techniques that deliver substantial radiation doses to the heart,” wrote study authors led by Naomi B. Boekel, MSc, of the Netherlands Cancer Institute in Amsterdam. “The absolute heart disease risks for women treated in the past are currently unclear, and it is not known which women might benefit from surveillance for heart disease.”

The new study assessed cardiovascular disease outcomes in a cohort of 14,645 breast cancer patients age ˂ 62 years (median age at diagnosis, 47 years) treated during the period between 1970 and 2009. Of these, 86% received radiation therapy, of whom 36% received IMC radiation. Approximately one-third of the cohort received chemotherapy, 58% of which was anthracycline-based. The median follow-up period was 14 years, and more than 3,400 patients were followed for at least 20 years. The results of the analysis were published in the British Journal of Cancer.

The lowest radiation dose to the heart was seen in women who received right-sided breast irradiation only, without IMC. Compared with that group, those who did receive IMC radiation had increased rates of any cardiovascular disease, with a hazard ratio (HR) of 1.56 (95% CI, 1.35–1.84). They also had increased rates of ischemic heart disease, with an HR of 2.36 (95% CI, 1.74–3.22); valvular heart disease, with an HR of 1.63 (95% CI, 1.18–2.24); and heart failure, with an HR of 1.82 (95% CI, 1.27–2.63).

Those women who received anthracycline-based chemotherapy also had increased rates specifically of valvular heart disease and heart failure, when compared with no chemotherapy. There appeared to be a “more than additive” effect when both IMC radiation and anthracyclines were administered with regard to heart failure, with an HR of 9.23 (95% CI, 6.01–14.18), compared with patients who received neither of these treatments.

The authors wrote that the risks for women treated today are likely lower, thanks to changes in practice. They noted, though, that these findings may be useful because some groups of breast cancer survivors may benefit from cardiac surveillance.

“As these older techniques were associated with a very large radiation dose to the heart, it was not surprising to see that this was correlated with an increased risk in cardiovascular disease over more than 2 decades of follow-up,” said David Wazer, MD, chairman of the Tufts University department of radiation oncology in Boston. “While these data are of interest and emphasize the absolute importance of minimizing radiation dose to the heart, particularly in the context of patients who are also receiving cardio-toxic chemotherapy, they likely do not reflect the risks faced in current practice.”