We have recently demonstrated that the use of human embryonic stem mesenchymal progenitors (hES-MP) is important in the generation of Clear Cell Sarcoma (CCS) and Angiomatoid Fibrous Histiocytoma (AFH) models harboring the EWSR1::ATF1/CREB1 translocations [13]. The gene discussed is ATF1; the disease is clear cell sarcoma.