[442] Diagnostic Value of Sox10 Immunohistochemical Staining for the Detection of Metastatic Melanoma in Sentinel Lymph Nodes

E Blochin, D Nonaka. New York University School of Medicine, New York, NY

Background: Sox10 is a pan-Schwannian and melanocytic marker superior to S-100 protein for its sensitivity and specificity (Am J Surg Pathol. 2008; 32(9):1291-8). S-100 protein, Melan A, and HMB-45 are commonly used for the detection of metastatic melanomas in the sentinel lymph nodes, with S-100 protein being the most sensitive. S-100 protein, however, can often be expressed by interdigitating dendritic cells and follicular dendritic cells of the lymph nodes. In a majority of cases, metastatic melanomas can be highlighted by a combination of the above three markers. Diagnostic problems may occur when there is no reaction to melanocyte specific markers, as is often the case with spindle cell and desmoplastic melanoma, or melanoma after multiple recurrences.
Design: 121 lymph nodes were studied from 80 consecutive sentinel lymphadenectomy procedures. Our protocol for melanoma sentinel lymph node work-up is comprised of 17 consecutive sections for each block, with H&E staining on the 1^st, 5^th, 9^th, 13^th and 17^th sections, and S-100 protein, HMB-45, and Melan A immunostaining on the 2^nd, 6^th and 10^th sections. This procedure yielded 33 lymph nodes positive for metastatic melanoma (PLNs) and 88 melanoma-negative lymph nodes (NLNs). After completion of this diagnostic work-up, Sox10 was stained on the 7^th section in all lymph nodes. The extent of staining was graded as follows: 1+, 1-25%; 2+, 25-50%; 3+, 50-75%; 4+, 75%.
Results: Diffuse (4+) Sox10 nuclear expression was seen in metastatic melanomas of all 33 PLNs (100%) while no melanoma was newly detected by Sox10 staining in any of the 88 NLNs. Melan A and HMB-45 were expressed in 29 (88%) and 27 (82%) of the lymph nodes. S-100 protein expression was detected without difficulty in 29 PLNs with 4+, 3+ and 1+ in 26, 2 and 1 lymph nodes. The remaining four lymph nodes contained a few HMB-45 and Melan A-positive single melanoma cells, which were, on S-100 protein stained slides, completely obscured by extensive S-100 protein-reactive dendritic cell population, but Sox10 highlighted these melanoma cells but not the dendritic cells. Metastatic desmoplastic melanoma in one lymph node was positive for Sox10 and S-100 protein, but negative for Melan A and HMB-45. Capsular nevus in three of the lymph nodes showed positive reaction to Sox10, S-100 protein, and Melan A, but not to HMB-45.
Conclusions: Owing to its excellent specificity and sensitivity Sox10 can replace the conventional panel of immunostains and be solely used for sentinel lymphadenectomy specimens for melanoma.
Category: Dermatopathology

Tuesday, March 10, 2009 8:00 AM

Platform Session: Section E, Tuesday Morning