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atypical Spitz tumor
Tuesday 8 February 2011
Definition: Atypical Spitz tumors (ASTs) are rare spitzoid neoplasms of uncertain biological behavior.
ASTs are an ill-defined and probably heterogenous group of melanocytic tumors that display histologic features seen in both Spitz nevi and melanomas. Their biological behavior cannot be reliably predicted.
Cytogenetics
There is no difference in chromosomal instability between AST patients with positive and negative sentinel lymph node biopsies.
The vast majority of chromosomal abnormalities observed in ASTs are not commonly found in melanomas, suggesting that AST may be a distinct clinical entity and raising additional questions regarding their malignant potential, prognosis, and clinical management.
Molecular biology
Germline mutations in BAP1 cause a familial tumor syndrome characterized by high penetrance for melanocytic tumors with distinct clinical and histologic features.
Melanocytic neoplasms in affected individuals harbored BRAF mutations, showed loss of BAP1 expression, and histologically resembled so-called "atypical Spitz tumors" (ASTs).
BRAF-mutated, BAP1-negative tumors are primarily located in the dermis and are composed entirely or predominantly of epithelioid melanocytes with abundant amphophilic cytoplasm and well-defined cytoplasmic borders.
Nuclei are commonly vesicular and exhibited substantial pleomorphism and conspicuous nucleoli.
The combination of BRAF mutation and loss of nuclear BAP1 expression thus characterizes a subset of ASTs with distinct histologic features.
References
Outcomes of Atypical Spitz Tumors With Chromosomal Copy Number Aberrations and Conventional Melanomas in Children. Gerami P, Cooper C, Bajaj S, Wagner A, Fullen D, Busam K, Scolyer RA, Xu X, Elder DE, Abraham RM, Prieto VG, Guitart J, Liu P, Pestova E, Barnhill RL. Am J Surg Pathol. 2013 Jun 20. PMID: 23797719
A Distinct Subset of Atypical Spitz Tumors is Characterized by BRAF Mutation and Loss of BAP1 Expression. Wiesner T, Murali R, Fried I, Cerroni L, Busam K, Kutzner H, Bastian BC. Am J Surg Pathol. 2012 Feb 24. PMID: 22367297
Copy number variations and clinical outcome in atypical Spitz tumors. Raskin L, Ludgate M, Iyer RK, Ackley TE, Bradford CR, Johnson TM, Fullen DR. Am J Surg Pathol. 2011 Feb;35(2):243-52. PMID: 21263245
