Overall survival is not impacted by whether a breast cancer tumor is on the left or right side in patients treated with breast-conserving surgery and adjuvant external beam radiation therapy, according to a new study published in the International Journal of Radiation Oncology • Biology • Physics (2014;90[2]:329-34).

Long-term follow-up of historic radiation therapy trials for breast cancer has 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.

Recent studies have suggested 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 commonplace.

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This study examined the impact of tumor laterality on overall survival in a modern cohort of patients from the National Cancer Database (NCDB). The NCBD is more than two times larger than the Surveillance, Epidemiology and End Results (SEER) database, and the NCBD contains data not found in SEER, including histopathologic data and specific treatment information such as sequencing of therapies, dose, technique (eg, intensity modulated radiation therapy vs brachytherapy), and target (eg, breast only vs breast and regional nodes).

This study analyzed 344,831 patients with a breast cancer diagnosis between 1998 and 2006. All patients had ductal carcinoma in situ (DCIS) or invasive carcinoma of any histologic subtype, and received external beam radiation therapy after breast-conserving surgery. Left breast tumors were present in 50.7% (174,956) of patients, and 49.3% (169,875) had tumors in the right breast. The median follow-up time for all patients was 6.04 years, and subset analyses were performed in patients with extended follow-up of 10 years or more.

The median whole breast radiation dose was 50.4 Gy in patients with DCIS, and 81% (33,733) of those patients received a boost to a median dose of 10 Gy. Of the patients with invasive disease, 85% (257,707) were treated with radiation therapy to the breast only with a median dose of 50.4 Gy.

Overall survival (OS) did not differ based on tumor laterality in all patients. At 5 years, overall survival was 92% in both left- and right-sided groups, and at 10 years, overall survival was 78% in both groups (P=.132). A multivariate analysis adjusted 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.

“The delivery of radiation therapy for breast cancer is markedly different today than it was several decades ago when the association between breast radiation, cardiac disease, and cardiac death was observed. Treatment planning and more advanced treatment techniques and technologies have reduced the risk to the heart,” said Charles E. Rutter, MD, lead author of the study and a fourth-year resident in the Department of Therapeutic Radiology at Yale School of Medicine in New Haven, Connecticut.