Genetic and regenerative contexts specify distinct soft tissue sarcoma identities from Twist2+ progenitors.

Soft tissue sarcomas (STS) comprise diverse mesenchymal malignancies whose developmental origins and mechanisms of subtype specification remain poorly understood. Whether distinct sarcoma subtypes can arise from a common progenitor through distinct oncogenic and tissue contexts has remained unresolved. Here, we show that skeletal muscle progenitors marked by expression of the Twist2 transcription factor generate distinct STS subtypes in response to defined genetic and microenvironmental cues. Activation of Kras together with Trp53 loss maintained a mesenchymal cell identity and drove highly penetrant undifferentiated pleomorphic sarcoma (UPS), whereas Trp53 loss or Hedgehog pathway activation in regenerating skeletal muscle preferentially induced fusion-negative rhabdomyosarcoma (FN-RMS). Single-nucleus RNA sequencing revealed fundamentally distinct tumor cell-state landscapes, with UPS enriched for mesenchymal-like states and FN-RMS spanning a continuum of myogenic differentiation states. Comparative analysis demonstrated that both models faithfully recapitulate the cellular hierarchies observed in their respective human STS subtypes. These findings reveal how oncogenic and microenvironmental contexts direct malignant lineage identity from a shared progenitor, providing a powerful platform for defining the developmental mechanisms and therapeutic vulnerabilities underlying STS subtype specification.