[464] Incidence and Description of Nevus Cell Rests and Their Distinction from Isolated Tumor Cells in Sentinel Lymph Nodes Removed for Melanoma Staging

Lisa D Duncan, Karyn L DeSouza, James M Lewis. University of Tennessee Medical Center, Knoxville, TN

Background: Sentinel lymph node excision is integral to melanoma surgical staging. Immunohistochemical (IHC) stains such as HMB-45, S-100, MART-1, tyrosinase, and melanoma triple stain are utilized to exclude metastatic disease. Individual IHC positive cells are challenging, warranting a clinically significant distinction between isolated tumor cells and benign nevus cell rests (NCR), as even isolated tumor cells represent N1 disease. In this study, the incidence and growth pattern of NCR in lymph nodes from various anatomic locations are described to form a basis of comparison for isolated IHC positive cells in sentinel lymph nodes removed for melanoma.
Design: Triple stain (HMB-45, MART-1, and tyrosinase combination) was performed on nodes from axillary (113), inguinal (44), cervical (184), and intraparotid (18) areas removed for non-melanoma related conditions to simulate regions typically sampled during melanoma sentinel node procedures. Additionally, thirteen cases with incidental NCR documented in the diagnosis field were retrieved from the Department of Pathology Anatomic Pathology Information System. Location, size, and histomorphology of NCR were recorded.
Results: Triple stain positive NCR were identified in 2 of 44 (4.5%) inguinal nodes (1.5 mm and 2.0 mm), 1 of 184 (0.5%) cervical nodes (0.5 mm), 1 of 113 (0.9%) axillary nodes (0.2 mm), and 0 of 18 intraparotid nodes. NCR in these cases had an intracapsular location, a spindle cell morphology mimicking fibroblasts, and were not perceptible on routine stains. NCR documented in the diagnosis field in 13 additional cases had 16 total NCR with a combined epithelioid and spindle morphology. Thirteen NCR were intracapsular and 3 were subcapsular with a size range of 0.5 – 9.0 mm.
Conclusions: Incidence of NCR is higher in the inguinal location relative to other anatomic locations studied. Rests identified only by IHC in our non-melanoma lymph node study cases have a spindle cell fibroblastic morphology. This finding in IHC stains in melanoma sentinel nodes can create diagnostic confusion with metastatic melanoma, emphasizing the importance of recognizing this morphologic pattern in NCR. Rests occurred as cell clusters measuring at least 0.2 mm and had a predominant intracapsular location, with only three having a subcapsular location. An isolated cell pattern was not observed in any of our study cases. Our results suggest that an isolated cell pattern identified in melanoma-specific IHC stains should be interpreted as metastatic melanoma.
Category: Dermatopathology

Tuesday, March 5, 2013 9:30 AM

Poster Session III # 50, Tuesday Morning


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