Adoption of FISH for Diagnosis of Melanoma
Jocelyn Moore, Carrie Fitzpatrick, Aliya N Husain, Thomas Krausz. University of Chicago, Chicago, IL
Background: The distinction between benign nevi and malignant melanoma (MM) can at times be difficult or impossible based on morphology and immunohistochemical analysis. Fluorescence in situ hybridization (FISH) is a molecular tool which has become diagnostically important in dermatopathology. Gerami et al (Am J Surg Pathol 2009 Aug;33(8):1146-56) were the first to demonstrate a four color FISH probe assay (RREB1, CCND1, CEN6 and MYB) which showed high sensitivity and specificity for distinguishing benign nevi from MM. The purpose of this study was to establish this FISH assay at our laboratory and confirm the utility of the assay using archival nevi and MM.
Design: The RREB1 probe was synthesized in-house via nick translation using a BAC clone (RP11-61016) labeled with SpectrumRed (Abbott Molecular Inc, IL). The other probes are commercially available. Specimens were selected on the basis of morphological diagnosis. Ten MM and 5 nevi were interrogated with FISH. The specimens were analyzed for number of signals corresponding to each probe and interpreted using published criteria (see Table 1). If the specimen fulfilled any of the criteria, it was considered a positive result.
Evaluation of Spitz nevi and atypical spitzoid tumors with this 4-probe set is ongoing. Currently, optimization of two additional FISH probes targeting 9p21 (p16) and 11p15 (HRAS) is underway. Benign nevi, MM, Spitz nevi and atypical spitzoid tumors will be interrogated with these additional probes.
Results: One of the MM cases failed due to tissue processing error. The remaining 9 MM cases showed positivity for one or more criteria for melanoma. Of the 5 nevi cases, none showed positivity for any of the criteria.
|Morphologic Diagnosis||>29% cells have >2 RREB1||>55% cells have RREB1>CEN6||>40% cells have MYB||>38% cells have > 2 CCND1|
|nevus, intradermal||N 3%||N 31%||N 9%||N 0%|
|nevus, intradermal||N 2%||N 8%||N 16%||N 8%|
|nevus, compound||N 0%||N 16%||N 14%||N 4%|
|nevus, compound||N 2%||N 8%||N 16%||N 14%|
|nevus, compound||N 8%||N 14%||N 6%||N 8%|
|MM, nodular||Y 82%||Y 90%||N 6%||N 12%|
|MM, nodular||Y 60%||Y 64%||Y 40%||N 16%|
|MM, nodular||Y 92%||Y 100%||Y 50%||Y 40%|
|MM, superficial spreading||Y 50%||Y 46%||Y 40%||N 12%|
|MM, spindle||Y 53%||N 40%||N 16%||N 5%|
|MM, metastatic||Y 80%||Y 80%||N 18%||N 20%|
|MM, metastatic||Y 54%||N 50%||N 20%||Y 84%|
|MM, metastatic||Y 70%||Y 58%||Y 62%||N 5%|
|MM, metastatic||Y 72%||Y 84%||N 18%||N 2%|