PDGFRB and desmoplastic small round cell tumor: The first clinical trial targeting PDGFR in DSRCT was using a small molecule inhibitor called SU101 or leflunomide and resulted in one patient out of 2 with DSRCT experiencing stable disease for more than 12 months before disease progression (36) Lenflunomide is not being developed further as an anti-sarcoma agent, but has been used as an immunosuppressant for treatment of rheumatoid arthritis (55).