Background: The ACOSOG Z0011 (Z11) trial demonstrated that in patients with nonpalpable axillary lymph nodes (LN) and one to two positive sentinel LN (SLN), axillary LN dissection (ALND) is unnecessary.JAMA 305:569–575, , Ann Surg 264:413–42,  The Z11 trial did not require preoperative axillary ultrasound (axUS). In many centers, preoperative axUS is part of the standard workup of a newly diagnosed breast cancer patient, but in light of the Z11 results, its role is now questioned. Methods: We retrospectively analyzed newly diagnosed breast cancer patients at two institutions. Inclusion criteria were patients with (1) no palpable lymphadenopathy, (2) abnormal axUS, (3) axillary LN metastasis confirmed preoperatively by axUS-lymph node needle biopsy, (4) no neoadjuvant therapy, and (5) ALND. LN disease burden was dichotomized as N1 versus N2-3. We examined relationships between clinicopathologic factors, including axUS characteristics, and LN disease burden. Results: Of 129 included cases, 67 had N1 disease (51.9%) and 62 had N2-3 disease (48.1%). Factors significantly associated with N1 disease were tumor size ≤2 cm (p = 0.012), nonlobular histology (p = 0.013), and one suspicious LN on axUS (p = 0.008). For patients with both tumor size on imaging ≤2 cm and one abnormal LN on axUS, only 27% had N2-3 disease (p = 0.007). Conclusions: More than half of patients without palpable adenopathy but with preoperative US-guided biopsy proven axillary LN metastases had N1 disease. For patients with both tumor size ≤2 cm and only 1 abnormal LN on axUS, 73% had N1 disease. This suggests that such patients, if they are otherwise analogous to Z11 patients, may undergo attempt at SLNB.
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