Axillary Micrometastases and Isolated Tumor Cells Are Not an Indication for Post-mastectomy Radiotherapy in Stage 1 and 2 Breast Cancer

Background. Randomized trials demonstrate equivalent locoregional control with sentinel lymph node biopsy (SLNB) or axillary lymph node dissection (ALND) for T1-2 micrometastatic breast cancer, but include few mastectomy patients. Consensus is lacking on indications for post-mastectomy radiotherapy (PMRT) in this population. Herein, we evaluate locoregional recurrence (LRR) in an unselected, modern cohort of T1-2 breast cancer patients with micrometastases or isolated tumor cells (ITCs; N0i+/N1mi) having a mastectomy. Methods. We identified patients with T1-2N0i+/N1mi breast cancer treated with mastectomy from January 2006 to December 2011. Recurrent, bilateral, and neoadjuvant cases were excluded. The primary outcome of interest was LRR. Results. Overall, 352 patients [211 (60%) with ITCs and 141 (40%) with micrometastases] were identified. 162 (46%) patients had SLNB alone and one node was positive in 295 (84%) cases; 31 (9%) patients had PMRT and 95% had systemic therapy. At a median 6 years of follow-up, the overall crude LRR rate was 2.8% (n = 9), with no axillary recurrences, and the crude LRR rate was 3.9% among those who had SNB alone. Those with LRR had a median age of 55 years, median tumor size of 1.7 cm, and ductal histology; the majority were high-grade (89%) and estrogen receptor positive (78%), with one positive node (89%). There was no association between LRR and receipt of PMRT (p = 0.4), SLNB versus ALND (p = 0.2), or number of positive nodes (p = 0.7) using the log-rank test. Conclusions. LRR was infrequent among T1-2N0i+/N1mi patients treated with mastectomy without PMRT, with no axillary failures, suggesting that PMRT or nodal radiotherapy are not routinely indicated in this population.