A Single-Cell Atlas Reveals Cancer Cell Plasticity and Stromal-Immune Remodeling in Uterine Carcinosarcoma Across Diverse Ancestries

Uterine carcinosarcoma (UCS) is an aggressive endometrial cancer defined by coexisting malignant epithelial and mesenchymal components, rapid metastatic dissemination, and poor therapeutic response. However, its cellular ecosystem remains poorly resolved, particularly in patients of African ancestry who are underrepresented in genomic datasets despite a disproportionate disease burden. Here, we generated a single-cell atlas of 15 primary and metastatic UCS specimens from a diverse cohort of 13 patients enriched for African ancestry, integrated with whole-genome sequencing. Malignant cells exhibited epithelial-like, mesenchymal-like, transitional, and stem/progenitor-like states within individual tumors that mapped to patient-specific copy number-defined subclones and RNA-velocity trajectories, supporting metaplastic state transitions. Compared to normal endometrium, primary tumors were enriched for epithelial-mesenchymal-transition (EMT), mTORC1, and glycolytic programs, whereas matched metastases show enhanced TNF-NF{kappa}B-associated invasive programs. The tumor microenvironment contained immunosuppressive myeloid states and diverse cancer-associated fibroblast (CAF) subsets, including pericyte-like and matrix-remodeling subsets that act as predicted communication hubs through chemokine and immune-checkpoint circuits. We found a CAF-centered CCL2-CXCL1/2-IL10 module linked to CD8 T-cell dysfunction and a TIGIT-CD96-PVR checkpoint module. These data define the UCS cellular ecosystem in which malignant plasticity is coupled to stromal-immune cell remodeling in a patient cohort of enriched ancestries and nominate stromal-immune axes for further therapeutic investigation.