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

"DOSE LEVELS FOR PATIENTS \> 21 YEARS OF AGE, Dose Level -1, prexasertib 105 mg/ m2 once every 14 days in 28 day cycles Dose Level 0, 60 mg/m2 prexasertib once every 21 days Dose Level 1, (STARTING) 80 mg/m2 prexasertib once every 21 days Dose Level 2, 105 mg/m2 prexasertib once every 21 days Dose Level 3, 105 mg/m2 prexasertib once every 21 days~DOSE LEVELS FOR PATIENTS ≤ 21 YEARS OF AGE Dose Level -1, prexasertib 150 mg/ m2 once every 14 days in 28 day cycles, Dose Level 0, 60 mg/m2 prexasertib once every 21 days, Dose Level 1, (STARTING) 80 mg/m2 prexasertib once every 21 days, Dose Level 2, 150 mg/m2 prexasertib once every 21 days, Dose Level 3, 150 mg/m2 prexasertib once every 21 days"

15 mg/m2 IV daily x 10 days in 21 day cycles