Abstract
Cancer remains a leading cause of death worldwide, with lineage plasticity emerging as a hallmark that drives therapy resistance and tumor progression by enabling cancer cells to alter identity and evade targeted therapies. Although genomic and transcriptomic aberrations correlate with lineage plasticity, the absence of pan-cancer markers to rapidly identify plastic subtypes has limited predictive utility. Homeobox (HOX) genes encode transcription factors that define tissue identity through distinct expression patterns, or HOX codes, in specific lineages. By analyzing multi-omics data, including 39 HOX genes from over 80,000 RNA-seq samples across 114 cancer types, we discovered that HOX code expression robustly represents cancer cell lineages and reveals multiple previously unrecognized lineage-plastic subtypes in prostate cancer, lung cancer, and acute myeloid leukemia (AML), each displaying altered HOX patterns compared to non-plastic subtypes. Differential analysis further identified RUNX1T1 as a novel and consistent marker of plasticity, elevated across all three cancer types and correlating with HOX code and lineage-plastic marker genes. We validated these correlations in bulk and single-cell RNA-seq from extensive preclinical and clinical cohorts and provided direct functional evidence that RUNX1T1 is required for lineage-plastic programs in prostate cancer. Using AI-based modeling, we identified NCOR/HDAC as RUNX1T1 binding partners forming a co-repressor complex that regulates HOX codes and plasticity. Finally, pharmacologic HDAC inhibition selectively suppressed the growth of plastic cells, revealing a novel therapeutic vulnerability. These findings establish ectopic RUNX1T1 as a pan-cancer biomarker and critical mediator of lineage plasticity and identify the RUNX1T1-HDAC complex as a druggable target.