Genome Med. 2026 May 28. doi: 10.1186/s13073-026-01676-0. Online ahead of print. ABSTRACT BACKGROUND: Extrachromosomal DNA (ecDNA) is a structural variant linked to poor prognosis in pediatric cancers. Patient-derived xenograft (PDX) models are crucial tools for cancer research, as they are believed to recapitulate the molecular features and intratumoral heterogeneity in patient tumors. However, ecDNA demonstrates unique evolutionary dynamics under selective pressure, and its behavior during PDX development remains largely uncharacterized. This study investigates the fidelity of PDX models in representing ecDNA from primary tumors. By analyzing ecDNA sequence composition and copy number conservation across pediatric solid cancers, we assess how well PDX models recapitulate the ecDNA landscape observed in human tumors. METHODS: AmpliconArchitect was used to analyze whole-genome sequencing (WGS) of 338 PDX models and 127 corresponding primary tumors. ecDNA status, sequence, copy number, and associated genes were compared between PDX models and their matched human tumors. Additionally, multiome RNA and ATAC single-cell sequencing of a PDX tumor enabled comparison of ecDNA intratumoral heterogeneity relative to similar data from the primary tumor. RESULTS: ecDNA in PDX models largely recapitulated oncogene amplifications observed in human tumors, with MYCN being the most frequently amplified. ecDNA status remained unchanged for a majority of the PDX models (105/127, 83%) compared to primary tumors, with 20% of previously ecDNA-negative cases acquiring ecDNA during PDX development. Consequently, ecDNA was more prevalent in the PDX models than in their corresponding human tumors (McNemar’s test, p = 0.00086). Detailed examination of ecDNA sequences in tumor-PDX pairs showed substantial conservation (67% with > 90% sequence overlap) but variable breakpoint concordance. Single-cell analysis demonstrated that rare ecDNA-positive cells from the primary tumor preferentially drive PDX tumor development. CONCLUSION: This study highlights the prevalence, oncogenic content, and conservation of ecDNA in PDX models relative to pediatric patient tumors. We observed that ecDNA frequently recapitulates oncogene amplifications found in human cancers, is generally preserved during PDX establishment, and reflects subtype-specific patterns across tumor types. These findings support the utility of PDX models in studying ecDNA biology in pediatric cancer progression and therapy. Longitudinal sampling during PDX tumor growth and under therapeutic pressure could provide insights into molecular evolution, clonal selection, and ecDNA-driven therapy resistance. PMID:42210429 | DOI:10.1186/s13073-026-01676-0

Trends Genet. 2026 Mar 31:S0168-9525(26)00038-7. doi: 10.1016/j.tig.2026.02.003. Online ahead of print. ABSTRACT The human ASXL gene family consists of ASXL1, ASXL2, and ASXL3, first described as the additional sex combs (Asx) in Drosophila. The encoded proteins scaffold BAP1-mediated histone H2A deubiquitination. ASXL genes are implicated in pre-cancerous, cancerous, and neurodevelopmental conditions. Truncating mutations predominate and were originally predicted to result in protein loss of function (LOF); however, mounting evidence from population genetics and in vitro studies supports gain-of-function (GOF) mechanisms. Sequence analysis suggests that such mechanisms require both escape from nonsense-mediated mRNA decay and removal of a putative C-terminal degron signal within ASXL proteins. We propose GOF as a generalized mechanism for ASXL mutations, resulting in increased protein stability and altered histone modifications, with implications for diagnosis and therapy for these medical conditions. PMID:41925445 | DOI:10.1016/j.tig.2026.02.003

bioRxiv [Preprint]. 2026 Mar 2:2026.02.27.708546. doi: 10.64898/2026.02.27.708546. ABSTRACT Extrachromosomal DNA (ecDNA) is a major driver of oncogene amplification, tumour heterogeneity and poor clinical outcomes [1-3], yet its detection relies on specialised genomic assays that are not integrated into routine diagnostics. Here, we show that ecDNA status can be inferred directly from standard haematoxylin and eosin-stained whole-slide pathology images. We develop an end-to-end, weakly supervised deep learning framework that aggregates thousands of high-magnification patches per slide with slide-level augmentation and interpretable attention. Across twelve cancer types from The Cancer Genome Atlas, the approach identifies tumours with genomic amplifications and, critically, distinguishes ecDNA-amplified from chromosomally amplified or non-amplified tumours, with the strongest signal in glioblastoma. Attention maps localise regions enriched for nuclei with altered chromatin intensity and texture, and predicted ecDNA status recapitulates its adverse association with survival. These results indicate that ecDNA amplifications leave reproducible histomorphologic foot-prints detectable by routine pathology, enabling scalable screening to prioritise tumours for confirmatory molecular testing. PMID:41847039 | PMC:PMC12991143 | DOI:10.64898/2026.02.27.708546

Nat Commun. 2025 Dec 10. doi: 10.1038/s41467-025-67257-8. Online ahead of print. ABSTRACT Estrogen receptor-positive breast cancer remains a leading cause of cancer-related death in women, with mortality largely driven by late recurrence of treatment-resistant disease. Loss of MLH1 promotes resistance to estrogen-targeting therapies by uncoupling cell cycle progression from estrogen regulation. Here, we show that even when MLH1 is abundantly expressed, aberrant cytoplasmic localization in a subset of tumor cells drives endocrine therapy resistance by enabling estrogen-independent growth. This resistance arises from failure to undergo robust cell cycle arrest in response to endocrine therapy, creating acute dependency on CDK4/6 activity. Consequently, CDK4/6 inhibitors induce strong regression in cells with cytoplasmic MLH1 compared to cells with nuclear MLH1. As cytoplasmic localization occurs in ~11% of ER+ patients, it represents a contributor to MLH1 dysregulation. Incorporating cytoplasmic MLH1 localization into diagnostics could guide the use of CDK4/6 inhibitors in this hard-to-treat subset. PMID:41372237 | DOI:10.1038/s41467-025-67257-8