Late-Stage Metastatic Melanoma Emerges through a Diversity of Evolutionary Pathways

Understanding the evolutionary pathways to metastasis and resistance to immune -checkpoint inhibitors (ICI) in melanoma is critical for improving outcomes. Here, we present the most comprehensive intrapatient metastatic melanoma dataset assembled to date as part of the Posthumous Evaluation of Advanced Cancer Environment (PEACE) research autopsy program, includ-ing 222 exome sequencing, 493 panel-sequenced, 161 RNA sequencing, and 22 single-cell whole-genome sequencing samples from 14 ICI-treated patients. We observed frequent whole-genome doubling and widespread loss of heterozygosity, often involving antigen-presentation machinery . We found KIT extra -chromosomal DNA may have contributed to the lack of response to KIT inhibitors of a KIT-driven mela-noma. At the lesion-level, MYC amplifi cations were enriched in ICI nonresponders. Single-cell sequencing revealed polyclonal seeding of metastases originating from clones with different ploidy in one patient. Finally, we observed that brain metastases that diverged early in molecular evolution emerge late in dis-ease. Overall, our study illustrates the diverse evolutionary landscape of advanced melanoma. SIGNIFICANCE: Despite treatment advances, melanoma remains a deadly disease at stage IV. Through research autopsy and dense sampling of metastases combined with extensive multiomic profi ling, our study elucidates the many mechanisms that melanomas use to evade treatment and the immune system, whether through mutations, widespread copy-number alterations, or extrachromosomal DNA.