[DNA copy number changes in the diagnosis of melanocytic tumors]

In the case of many tumors, the development of cancer is associated with a loss of control over genomic integrity, resulting in alterations, determined by selection, of the genome of the cancer cells. Comparative genomic hybridization (CGH) is a method that can be used to assess the entire genome of tumor cells for the presence of changes in DNA copy number. CGH analysis has revealed that melanomas differ from melanocytic nevi in the presence of frequent chromosomal aberrations. CGH analysis of benign melanocytic tumors typically shows no clonally expanded chromosomal aberrations, while in the vast majority of melanomas gains and losses of particular chromosomes are found. As an exception, Spitz nevi show an increased copy number of chromosome 11p in about 20% of cases, something not found in melanoma. These marked differences between the aberration patterns of melanomas and melanocytic nevi can be exploited during differential diagnosis of melanocytic tumors in which histopathologic assessment yields equivocal results. In addition, it has also been shown with the aid of CGH and mutation analysis that melanomas are not a homogenous disease, but rather a group of genetically different tumors. A study checking for correlations between the chromosomal alterations in melanocytic tumors not classified at diagnosis and the course of illness in patients is currently under way.