Background: As tumor biology takes precedence over anatomic staging to determine breast cancer (BC) prognosis, there is growing interest in limiting axillary surgery. There is a need for tools to identify patients at the lowest risk of harboring axillary lymph node (ALN) disease, to determine when omission of sentinel lymph node biopsy (SLNB) may be appropriate. We examined whether a nomogram using preoperative axillary ultrasound (axUS) findings, clinical tumor size, receptor status, and grade to calculate the probability of nodal metastasis (PNM) has value in surgical decision making. Methods: This was a retrospective analysis of female patients (February 2011–October 2014) with invasive BC who underwent preoperative axUS and axillary surgery. Cases with locally advanced BC, neoadjuvant treatment, or bilateral BC were excluded. PNM was calculated for each case. Using various PNM thresholds, the proportion of cases with ALN metastasis on pathology was examined to determine an optimal PNM cut-point to predict ALN negativity. Results: Of 357 included patients, 72% were node-negative on surgical staging, and 69 (19.6%) had a PNM < 9.3%. Of these 69 patients, 6 had ALN metastasis on surgical pathology, yielding a false negative rate (FNR) of 8.7% for predicting negative ALN when a PNM threshold of < 9.3% was used. Conclusion: A nomogram incorporating axUS findings and tumor characteristics identified a sizeable subgroup (19.6%) in whom ALN was predicted to be negative, with an 8.7% FNR. Surgeons can use this nomogram to quantify the probability of ALN metastasis and select patients who may benefit from omitting SLNB.
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