A Study of the Drugs Prexasertib, Irinotecan, and Temozolomide in People With Desmoplastic Small Round Cell Tumor and Rhabdomyosarcoma

Inclusion Criteria: * Consent/Assent: all patients and/or their parents or legally authorized representatives must sign written informed consent; assent, when appropriate, will be obtained according to institutional guidelines * Age: patients must be ≥12 months of age at the time of study enrollment * Diagnosis: patients must have histologically documented locally advanced or metastatic desmoplastic small round cell tumor or rhabdomyosarcoma (confirmed at MSK) * Therapeutic options: patient's current disease state must be one which has failed standard therapy and for which there is no known curative therapy * Disease Status: patients must have measurable disease based on RECIST 1.1 * Performance level: Karnofsky ≥ 50% for patients \> 16 years of age and Lansky ≥ 50 for patients ≤ 16 years of age * Prior Therapy: patients may have had any number of prior therapies, but must have recovered from the acute toxic effects of all prior anti-cancer therapy (other than alopecia) as described below and must meet the following minimum duration from prior anti-cancer directed therapy prior to enrollment °patients who have previously received irinotecan and/or temozolomide will be allowed * 21 days must have elapsed after the last dose of cytotoxic or myelosuppressive chemotherapy * 7 days must have elapsed after the last dose of anti-cancer agents not known to be myelosuppressive * 14 days must have elapsed after radiation therapy, and toxicity related to prior radiation therap…