Wednesday 16 June 2004
UI:337 - Spitz nevus
dysplastic nevi with features of Spitz nevus
pigmented spindle cell nevus
desmoplastic Spitz nevus
plexiform spindle cell nevus - deep-penetrating nevus
cellular blue nevus
epithelioid cell histiocytoma
copy number increases of chromosome 11p paralleled by mutations in the HRAS oncogene
The isolated copy number increases of chromosome 11p in Spitz nevi raised the question as to which gene on 11p drives the selection forces that led to the accumulation of extra copies of that chromosomal arm.
HRAS-mutated SPitz tumor (20871217)
HRAS belongs to the family of ras genes, which contains the two additional members KRAS and NRAS. HRAS maps to the distal end of chromosome 11p, and cancers with mutations in ras gene frequently amplify the mutated allele. Sequencing of the two hot spots for mutations in HRAS, codons 12, 13, and 61, and found that about 70% of the Spitz nevi with 11p copy number increases showed oncogenic mutations (Bastian et al., 2000b).
In a study, one out of 21 Spitz nevi with a normal copy number of 11p that had a mutation of HRAS. These findings suggest that HRAS is at least one target of the selection forces that lead to increasing copy numbers.
NRAS mutations are found in about 25% of primary cutaneous melanomas (see Herlyn and Satyamoorthy, 1996 for a review).
Interestingly, HRAS itself is rarely mutated in melanoma (van Elsas et al., 1996; Jiveskog et al., 1998). HRAS mutations have been described in Spitz naevi, but thus far never in melanoma. Thus far no HRAS mutations have been reported in spitzoid melanomas.
There is no evidence that cases with HRAS mutations were at risk to progress to melanoma.
Mutation analysis to differentiate between Spitz naevus and spitzoid melanoma
A minor part of the Spitz naevi is unique among melanocytic tumours for having a single gain of 11p (26%) and/or HRAS mutations, the latter occurring in up to 29% of cases.
Demonstration of either a HRAS mutation or a single 11p gain therefore seems indicative of benign behaviour.
In difficult to diagnose spitzoid lesions, so-called Spitzoid tumours of uncertain malignant potential, assessment of one of these cytogenetic aberrations could be of help in making a more accurate diagnosis.
The observation that the 11p copy number increase indicating an isochromosome 11p was not seen in over 300 melanomas, and melanoma cell lines studied so far further argues against the possibility that these Spitz nevi are precursors to melanoma. (Bastian, 2003; 12789284)
HRAS-mutated Spitz tumors: A subtype of Spitz tumors with distinct features. van Engen-van Grunsven AC, van Dijk MC, Ruiter DJ, Klaasen A, Mooi WJ, Blokx WA. Am J Surg Pathol. 2010 Oct;34(10):1436-41. PMID: 20871217
Harvell JD, Kohler S, Zhu S, Hernandez-Boussard T, Pollack JR, van de Rijn M. High-resolution array-based comparative genomic hybridization for distinguishing paraffin-embedded Spitz nevi and melanomas. Diagn Mol Pathol. 2004 Mar;13(1):22-5. PMID: 15163005
Maldonado JL, Timmerman L, Fridlyand J, Bastian BC. Mechanisms of cell-cycle arrest in Spitz nevi with constitutive activation of the MAP-kinase pathway. Am J Pathol. 2004 May;164(5):1783-7. PMID: 15111324
Bogdan I, Burg G, Boni R. Spitz nevi display allelic deletions. Arch Dermatol. 2001 Nov;137(11):1417-20. PMID: 11708943