Internal mammary nodal irradiation in conservatively-managed breast cancer patients: is there a benefit?

PURPOSE: Recent randomized trials have demonstrated a significant benefit to postmastectomy radiation in node-positive breast cancer patients. The contribution of internal mammary nodal radiation (IMNR) to this benefit remains controversial, and in conservatively-treated patients (CS + RT), may compromise cosmesis and contribute to morbidity. The purpose of this retrospective analysis is to evaluate outcome as a function of IMNR in a cohort of breast cancer patients treated with CS + RT. PATIENTS AND METHODS: Between January 1970 and December 1990, 984 patients with invasive breast cancer were treated at our facility with CS + RT, and serve as the base for this study. Of these patients, 399 patients had pathologically-negative lymph nodes, 167 (17%) had pathologically-involved lymph nodes, and 381 did not undergo lymph node dissection. The majority of node-positive patients received adjuvant systemic therapy (94%) and were treated with tangential fields matched to a separate supraclavicular field (95%) with or without IMNR. For this analysis, patients were divided into two groups: those treated by intentionally targeting the internal mammary nodes (IM-yes, n = 535) and without intentionally targeting the internal mammary nodes (IM-no, n = 411). In the IM-no group, the medial border was typically placed at midline. The decision not to use a separate internal mammary field was a result of a change in treatment policy over time, and generally not based on number of nodes or tumor location.
RESULTS: As of August 1998, with a median follow-up of 13 years, the overall survival at 10 years is 76%, the distant disease-free survival is 81%, and the breast relapse-free survival is 88%. There were no significant differences between the IM-yes and IM-no groups with respect to age, ER/PR status, or use of adjuvant chemotherapy or hormone therapy. There were more patients with T2 tumors, positive nodes, medial lesions, indeterminate margins, and slightly longer follow-up in the IM-yes group compared to the IM-no group. Although there was a trend toward better outcome in the IM-no group, there were no significant differences between the IM-yes and IM-no groups with respect to overall survival (72% IM-yes vs. 84% IM-no, p = NS) or distant metastasis-free survival (64% IM-yes vs. 82% IM-no, p = NS). Subset analysis showed no benefit in the IM-yes group regardless of age, number of nodes, or location.
CONCLUSION: In this retrospective analysis, no benefit could be attributed to IMNR in conservatively-treated breast cancer patients, even if node-positive or medial in location. Until results of an ongoing EORTC randomized trial addressing this issue are available, these data suggest that it is acceptable to continue to treat node-positive conservatively-managed patients to tangential fields usually matched to a supraclavicular field, but without a separate internal mammary field.