Mutational concordance between primary and metastatic melanoma: a next-generation sequencing approach

Background: Cutaneous malignant melanoma (CMM) is one of the most common skin cancers worldwide. Limited
information is available in the current scientific literature on the concordance of genetic alterations between primary
and metastatic CMM. In the present study, we performed next-generation sequencing (NGS) analysis of the main
genes participating in melanoma pathogenesis and progression, among paired primary and metastatic lesions of
CMM patients, with the aim to evaluate levels of discrepancies in mutational patterns.
Methods: Paraffin-embedded tumor tissues of the paired lesions were retrieved from the archives of the institutions
participating in the study. NGS was performed using a specific multiple-gene panel constructed by the Italian
Melanoma Intergroup (IMI) to explore the mutational status of selected regions (343 amplicons; amplicon range:
125–175 bp; coverage 100%) within the main 25 genes involved in CMM pathogenesis; sequencing was performed
with the Ion Torrent PGM System.
Results: A discovery cohort encompassing 30 cases, and a validation cohort including eleven Sardinian patients with
tissue availability from both the primary and metachronous metastatic lesions were identified; the global number of
analyzed tissue specimens was 90. A total of 829 genetic non-synonymous variants were detected: 101 (12.2%) were
pathogenic/likely pathogenic, 131 (15.8%) were benign/likely benign, and the remaining 597 (72%) were uncertain/
unknown significance variants. Considering the global cohort, the consistency in pathogenic/pathogenic like mutations
was 76%. Consistency for BRAF and NRAS mutations was 95.2% and 85.7% respectively, without statistically
significant differences between the discovery and validation cohort.
Conclusions: Our study showed a high level of concordance in mutational patterns between primary and metastatic
CMM, especially when pathogenic mutations in driver genes were considered.