Background: Sentinel lymph node biopsy (SLNB) is the standard approach for the axillary region in early breast cancer patients with clinically negative nodes. The present study investigated patients with false-negative sentinel nodes in intraoperative frozen sections (FNSN) using real-world data. Methods: A case–control study with a 1:3 ratio was conducted. FNSN was determined when sentinel nodes (SNs) were negative in frozen sections but positive for metastasis in formalin-fixed paraffin-embedded (FFPE) sections. The control was defined as having no metastasis of SNs in both frozen and FFPE sections. Results: A total of 20 FNSN cases and 60 matched controls from 333 SLNB patients were enrolled between April 1, 2005, and November 31, 2009. The demographics and intrinsic subtypes of breast cancer were similar between the FNSN and control groups. The FNSN patients had larger tumor sizes on preoperative mammography (P = 0.033) and more lymphatic tumor emboli on core biopsy (P < 0.001). Four FNSN patients had metastasis in nonrelevant SNs. Another 16 FNSN patients had benign lymphoid hyperplasia of SNs in frozen sections and metastasis in the same SNs from FFPE sections. Micrometastasis was detected in seven of 16 patients, and metastases in nonrelevant SNs were recognized in two patients. All FNSN patients underwent a second operation with axillary lymph node dissection (ALND). After a median follow-up of 143 months, no FNSN patients developed breast cancer recurrence. The disease-free survival, breast cancer-specific survival, and overall survival in FNSN were not inferior to those in controls. Conclusions: Patients with a larger tumor size and more lymphatic tumor emboli have a higher incidence of FNSN. However, the outcomes of FNSN patients after completing ALND were noninferior to those without SN metastasis. ALND provides a correct staging for patients with metastasis in nonsentinel axillary lymph nodes.
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