Track

Clinical Studies

Abstract

Accurate pathological evaluation of sentinel lymph nodes (SLNs) is essential for cancer staging, yet benign epithelial inclusions can closely mimic metastatic carcinoma. Among these, squamous epithelial inclusions are rare and may be mistaken for metastatic cystic squamous cell carcinoma (mcSCC), especially in the neoadjuvant setting. We reviewed SLN and lymph node biopsies with histologically confirmed squamous epithelial inclusions from 2009–2025 at Massachusetts General Hospital and Brigham and Women’s Hospital. Twenty lymph nodes from seventeen patients (age 20–80 years; median 59; F:M = 7.5:1) were identified. Most (17/20, 85%) were axillary SLNs sampled for confirmed or suspected breast lesions; others were cervical SLN (1/20, 5%) or from isolated lymphadenopathy (2/20, 10%). Of 13 patients with full histories, 12 (92%) had prior ipsilateral breast or axillary procedures. Findings that supported the benign nature of the squamous inclusions include bland cytomorphology, full-thickness epidermoid differentiation, and presence of heterotypic glandular or follicular elements. Squamous epithelial inclusions are an uncommon but consequential mimic of mcSCC in SLN evaluation. Recognition of their histologic features, awareness of prior instrumentation, and consideration of anatomic drainage patterns are critical to avoiding overdiagnosis during cancer staging.