[549] Fluorescence In Situ Hybridization (FISH) Reliably Distinguishes Tumour Cells of Benign Melanocytic Nevi from Those of Metastatic Melanoma

Michael Sidiropoulos, Ziad Hindi, Ayman Al-Habeeb, Danny Ghazarian, Kenneth J Craddock. University of Toronto, Toronto, ON, Canada; University Health Network, Toronto, ON, Canada

Background: Malignant melanoma can be difficult to distinguish from a benign melanocytic lesion by histology. In previous studies, 3 chromosomal aberrations have been identified that are common in malignant melanoma but not found in benign nevi. Previous literature has been encouraging but not conclusive on the utility of fluorescence in situ hybridization (FISH) in assisting in diagnosis. In this study, we investigated the sensitivity and specificity of FISH to distinguish between benign nevi and metastatic melanomas to lymph nodes.
Design: Multicolour FISH was performed using a commercially available probeset (Abbott Laboratories, Abbott Park, IL), on formalin-fixed, paraffin-embedded tissue samples from 40 tumours: 20 benign melanocytic nevi, and 20 metastatic melanomas within lymph nodes, as determined by histologic assessment. Fluorescent signals for each probe were enumerated by 2 observers in 30 cells each per lesion. An algorithm using signal counts from a combination of 4 probes targeting chromosome 6p25 (containing RREB1 gene), 6 centromere (CEP6), 6q23 (containing MYB gene), and 11q13 (containing CCND1 gene) was used as suggested by the manufacturer. The following criteria were used: (1) the average CCND1 or MYB signals per nuclei is greater than or equal to 2.5 or (2) percent loss of MYB relative to CEP6 is greater than or equal to 31% or (3) the percentage of abnormal nuclei for RREB1 is greater than or equal to 63%. If at least one of the three criteria were met, the specimen was designated FISH positive. If none of the criteria were met, the specimen was designated as FISH negative.
Results: Of the 20 metastatic melanomas assessed, 18 were FISH positive. FISH detected significant abnormal nuclei for RREB1 in 17/20 cases (85%) and significant MYB loss in 12/20 cases (60%). Average signals per nuclei greater than 2.5 for CCND1 and MYB were present in only 7/20 (35%) and 4/20 (20%) cases respectively. All 20 benign nevi were FISH negative. Overall, the FISH test showed a sensitivity of 90% and specificity of 100%, in diagnosis of metastatic melanoma to lymph nodes.
Conclusions: These results provide further compelling evidence for the utility of multicolour FISH directed against 6p25 (RREB1), centromere 6, 6q23 (MYB), and 11q13 (CCND1), as an aid in determining malignant behaviour in melanocytic lesions.
Category: Dermatopathology

Wednesday, March 21, 2012 1:00 PM

Poster Session VI # 107, Wednesday Afternoon

 

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