Epithelium Involving Bilateral Axillary Lymph Nodes: Metastasis, Misplaced, or Mullerian

During breast cancer staging, histological evaluation of axillary sentinel lymph nodes (SLN) is usually straightforward. However, the exact characterization of a small epithelial deposit in an SLN can be challenging, especially during the frozen section examination. We report the first case of endosalpingiosis involving bilateral axillary lymph nodes. We review published literature on axillary endosalpingiosis and discuss the differential diagnosis of small epithelial deposits in an axillary SLN. Pathologists should consider benign epithelial rests and displaced epithelium as differential diagnoses for the microscopic epithelial nodal deposit, especially during the frozen section examination.