Extrachromosomal DNA (ecDNA) is a large circular species of DNA that often mediates oncogene amplification. As published in Cell Genomics in 2024, we characterized ecDNAs across advanced cancers in the Long POG cohort (n = 189; O’Neill et al. 2024, doi:10.1016/j.xgen.2024.100674) using both short- and long-read whole-genome sequencing (WGS) approaches. Work is ongoing in cervical cancer (n = 118; HIV+ Tumor Molecular Characterization Project (HTMCP) cohort) to compare ecDNAs containing both human and human papillomavirus (HPV) DNA to those containing only human DNA, in terms of their genomic and epigenomic features.