ATR and Ewing sarcoma: In particular, fusion-positive Ewing sarcoma cells (A673 and TC32) exhibit exquisite sensitivity to THZ531, a CDK12/13 inhibitor, resulting in the downregulation of the homologous recombination (HR) and DNA damage checkpoint genes, including BRCA1, ATR, FANCl, and FANCD2 [34, 35].