Abstract LB-349: Characterization of copy number variations in atypical Spitz tumors

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Abstract Background and Objective: Atypical Spitz tumors (AST) are rare spitzoid neoplasms with uncertain metastatic potential with overlapping histological features between Spitz nevi and spitzoid melanoma. Histopathological and clinical management of ASTs is complex and controversial. About 50% of ASTs have positive SLNB, but only 1.5% of ASTs metastasize. Our study was designed to characterize genetic abnormalities that can help to differentiate ASTs from melanoma or Spitz nevi. Methodology: We examined copy number variation in formalin-fixed paraffin-embedded (FFPE) samples using 44k array CGH from Agilent. Tissue blocks from 17 patients with AST (9 with positive sentinel lymph nodes biopsy (SLNB), 7 with negative SLNB, 1 with distant metastasis), 8 patients with Spitz nevi, and 4 patients with melanoma (3 spitzoid, 1 superficial spreading) were used for analysis. Results: We found chromosomal abnormalities in 7/17 ASTs, including 1 AST with distant metastases, spitzoid melanoma with positive SLNB, metastatic spitzoid melanoma, and invasive melanoma. Nine of 17 (53%) ASTs did not have chromosomal instability similar to the majority of Spitz nevi, and 7 of 16 (47%) of ASTs had gross chromosomal abnormalities, including those that are uncommon in invasive melanomas. Among Spitz nevi only one had amplification of the 11p15.5-p12 containing HRAS, a candidate region previously reported as amplified in Spitz nevi. Two ASTs with positive SLNB and one AST with negative SLNB share an amplification of an overlapping region on 1p containing oncogene JUN. Two ASTs have amplification and 2 ASTs have deletion of the whole chromosome 9, containing CDKN2A gene. Some chromosomal abnormalities (loss of 8p and 9, and gain of 8q (cMYC)) found in metastatic AST are common for invasive melanomas. On the other hand, metastatic AST did not have the most frequent changes involving chromosome 6 and 11q, which are loci for FISH probes recently developed to distinguish malignant melanoma from benign melanocytic lesions. In addition, there was no difference in chromosomal instability between AST patients with positive and negative SLNBs, questioning the value of SLNB in the management of ASTs. Spitzoid melanoma with positive SLNB had only deletion of chromosome 9, and metastatic spitzoid melanoma had deletion of 11q13 region (CCDN1) similar to invasive melanoma. No other common melanoma chromosomal abnormalities were detected in these two spitzoid melanomas. Conclusions: Array CGH analysis can be used to divide melanocytic lesions of uncertain biologic potential into three groups: AST without chromosomal aberrations, AST with chromosomal aberrations, and invasive melanoma. Tumor progression is associated with increasing frequency of complex structural and numerical aberrations in the digital karyotype. Considering this fact, ASTs with chromosomal abnormalities, although not similar to melanoma, can raise several questions regarding their malignant potential, prognosis, and clinical management. ASTs without chromosomal imbalances are best regarded as Spitz nevi with variably atypical histological features. An existing panel of limited FISH probes can fail to detect fatal metastatic AST and other melanocytic lesions. A more comprehensive, genome-wide approach to assess chromosomal abnormalities may have the potential to offer greater sensitivity and specificity to identify melanocytic lesions with uncertain malignant potential. Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr LB-349.