Radiation field design and regional control in sentinel lymph node-positive breast cancer patients with omission of axillary dissection.

BACKGROUND: Randomized data suggest that axillary clearance is not necessary in select, clinically lymph node-negative women with positive sentinel lymph node (SLN) biopsies (SLNBs) who undergo breast-conserving surgery or receive whole-breast radiotherapy and systemic therapy. The additional value of axillary radiotherapy in these patients is unknown. METHODS: The authors identified 326 patients with positive SLNBs who underwent breast-conserving surgery without axillary lymph node dissection from 1997 to 2009. SLN tumor deposits measured ≤0.2 mm in 58% of patients, 0.3 to 2.0 mm in 35% of patients, and >2 mm in 7% Patients. Ninety-three percent of patients received adjuvant radiotherapy. Radiation fields were categorized as standard tangents, high tangents, comprehensive (tangents plus supraclavicular), or partial breast to reflect coverage of the axilla. Standard tangents included both prone and supine positions. Regional failure was defined as recurrence in the ipsilateral supraclavicular, axillary, or internal mammary lymph nodes. RESULTS: The median follow-up was 55 months (range, 1-158 months). The 4-year rates of regional control, local control, disease-free survival, and overall survival were 99%, 98%, 95%, and 91%, respectively. Three patients had regional recurrences. Two of those patients received adjuvant radiotherapy with standard supine tangents, and 1 patient did not receive radiotherapy. No regional recurrences occurred among 66 patients who received radiotherapy in the prone position. CONCLUSIONS: Regional control was high (99% at 4 years) in patients who had low-volume SLN disease who did not undergo axillary dissection, regardless of whether the axilla was irradiated. Whole-breast radiation alone, including in the prone position, is sufficient treatment after breast-conserving surgery for select patients with tumor-containing SLNs who omit axillary dissection.