No Increase In Cardiac Mortality from Breast Radiotherapy

October 30, 2014 Vivek K. Mehta, MD

Patients that I see routinely ask me about the heart-related side effects from breast treatment.

Today, I can provide them with even greater evidence that the techniques that we use today are safer and have less risk of cardiac injury. According to a study published in the October 1, 2014 issue of the International Journal of Radiation Oncology • Biology • Physics (Red Journal), the official scientific journal of the American Society for Radiation Oncology (ASTRO), the survival from breast cancer is the same regardless of whether you were treated with radiation to your left or right breast mound.

Many studies over many decades have shown that breast cancer patients treated with radiation therapy have improved local-regional recurrence, and breast cancer-specific survival after breast-conserving surgery and overall survival (OS) after mastectomy. The media has focused its attention on long-term follow-up of historic radiation therapy trials for breast cancer which demonstrated a potential increase in cardiac mortality. However, these studies used earlier modes of radiation therapy including Cobalt and orthovoltage radiotherapy, and did not employ CT-based planning, which allows for greater cardiac avoidance. Three recent studies suggest that cardiac mortality has not been greater for patients treated for left-sided breast cancer since the 1980s, when techniques allowing for greater cardiac avoidance became more commonplace1-3.

The study “Breast Cancer Laterality Does Not Influence Survival in a Large Modern Cohort: Implications for Radiation-Related Cardiac Mortality” examines the impact of tumor laterality on overall survival in a modern cohort of patients from the National Cancer Database (NCDB).

This study reviewed 344,831 patients diagnosed with breast cancer between 1998 and 2006 who received external beam radiation therapy after breast-conserving surgery. About half the patients were treated on the right side and the other half received treatment on the left side. The median follow-up time for all patients was approximately 6 years, and subset analyses were performed in patients with follow-up of 10 or more years.

The median whole breast radiation dose was approximately 50.4 Gy and many patients received a boost of 10-12 Gy to the cavity.

Overall survival (OS) did not differ based on tumor laterality in all patients. At five years, overall survival was 92 percent in both left- and right-sided groups, and at 10 years, overall survival was 78 percent in both groups (p=.132). A multivariate analysis with Cox regression was performed to adjust for demographic and pathologic factors that could impact OS, including age, grade, estrogen receptor status, tumor size, number of positive nodes, receipt of chemotherapy and receipt of endocrine therapy. The multivariate analysis showed no difference in OS by tumor laterality (Hazard Ratio 1.002, 95 percent Confidence Interval, p=.874).

This study demonstrates that with modern techniques there does not appear to be an increase in cardiac mortality as a result of radiation treatment for breast cancer. At the Swedish Cancer Institute, we are constantly working to improve the treatment of our patients. We have worked to integrate the ABC device as a method of reducing cardiac dose and employ a variety of specialized planning techniques as well.

1 Darby SC, McGale P, Taylor CW, et al. Long-term mortality from heart disease and lung cancer after radiotherapy for early breast cancer: prospective cohort study of about 300,000 women in US SEER cancer registries. Lancet Oncol 2005;6:557-565.

2 Giordano SH, Kuo YF, Freeman JL, et al. Risk of cardiac death after adjuvant radiotherapy for breast cancer. J Natl Cancer Inst 2005;97: 419-424.

3 Hooning MJ, Botma A, Alerman BM, et al. Long-term risk of cardiovascular disease in 10-year survivors of breast cancer. J Natl Cancer Inst 2007;99:365-375.

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