Increased frequency of minimal homozygous deletions is associated with poor prognosis in primary malignant melanoma patients

Identification of prognostic melanoma-associated copy number alterations (CNAs) is still an area of active research. Here, we investigated by high-resolution array comparative genomic hybridization (aCGH) a cohort of 31 paraffin-preserved primary malignant melanomas (MMs), whose prognosis was not predictable on the basis of conventional histopathological parameters. Although we identified a variety of highly recurrent sites of genomic lesions, the total number of CNAs per patient was not a discriminator of MM outcome. Furthermore, validation of aCGH by quantitative PCR on an extended population of 65 MM samples confirmed the absence of predictive value for the most recurrent CNA loci. Instead, our analysis revealed specific prognostic potential of the frequency of homozygous deletions (representing less than 3\% of the total CNAs on average per sample), which was strongly associated with sentinel lymph node (SLN) invasion (P = 0.003), and distant metastasis (P = 0.003). Increased number of homozygous deletions was also indicative of poor patient survival (P = 0.01), both in our samples and in an independent validation of public dataset of primary and metastatic MMs. Moreover, we identified 77 hotspots of minimal common homozygous deletions, enriched in genes involved in cell adhesion processes and cell-communication functions, which preferentially accumulated in primary MMs showing the most severe outcome. Therefore, specific loss of gene loci in regions of minimal homozygous deletion may represent a pivotal type of genomic alteration accumulating during MM progression with potential prognostic implication.