This retrospective 3-institution study evaluated whether the radiation dose delivered to the axilla (initially involved lymph nodes and levels I–III) affects oncologic outcomes in 132 cN1–2a breast cancer patients who converted to ypN0 on SLNB after primary systemic therapy (PST), followed by breast surgery without ALND and postoperative radiotherapy (median follow-up 79 months).
At 5 years, axillary recurrence-free survival was 98.4% (only 3 axillary recurrences, 2.3%), DFS was 90.1%, and OS was 96.2%. No significant association was found between axillary radiation dose and DFS; non-pathologic complete response (HR 3.78, p=0.041) and total mastectomy (HR 4.43, p=0.006) were the only independent predictors of worse DFS.
- Retrospective design with inherent selection bias across three institutions. - Relatively small sample (n=132) limits statistical power to detect dose-outcome relationships. - No prospective dose-assignment or randomization; actual dose thresholds for safe de-escalation remain undefined.
In cN+ breast cancer patients downstaged to ypN0 by SLNB after PST, excellent axillary control was achieved even at lower axillary radiation doses, suggesting tailored de-escalation of axillary RT may be feasible. Clinicians should note that non-pCR and mastectomy — not radiation dose — drove worse DFS, but prospective data are still needed before changing dose prescriptions.
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