Phylogenetic Analyses of Melanoma Reveal Complex Patterns of Metastatic Dissemination

Subpopulations of cells in a primary melanoma can disseminate and establish metastases. Still, the precise ancestral relationship between primary tumors and their metastases is not well understood. Using whole-exome sequencing (for discovery) and targeted sequencing (for validation), we analyzed mutation patterns of primary melanomas and two or more metastases in each of 8 patients to determine their phylogenetic relationships, profiling a total of 31 total tumors. The resulting data show that in 6 of 8 cases, genetically unique cell populations in the primary metastasized in parallel to distinct anatomic sites, rather than sequentially. These data also indicate that individual metastases were sometimes founded by multiple cell populations of the primary that were genetically distinct.