Tagraxofusp in Pediatric Patients With Relapsed or Refractory CD123 Expressing Hematologic Malignancies

Dose will be assigned at study entry. Give IV over 15 minutes.

"30 mg/m\^2 will be given IV over 30 minutes on days 1-5.~Infusion will start 30 minutes after start of tagraxofusp on days 4 and 5."

2000 mg/m2 intravenously will be given daily over 1-3 hours for 5 days on days 1 through 5. Infusion will begin 4 hours after start of fludarabine. Because of an increased risk of neurotoxicity, it is recommended that IT cytarabine be separated from high dose IV cytarabine administration by at least 24 hours on C1D1.

"* 20 mg/m2/day divided BID (max 40 mg/day) given orally on days 1 through 5 and 15 through 19. The two doses should be separated by at least 8 hours.~* Any oral formulation of dexamethasone is acceptable.~* IV may be given if oral formulation is not tolerated"

"* 1.5 mg/m2 (maximum dose 2 mg) given intravenously as an IV push over 1-5 minutes or infusion via minibag as per institutional policy on days 1, 8, 15, and 22.~* Infusion will start 30 minutes after start of tagraxofusp on day 8."

"* 75 mg/m2 subcutaneously or intravenously will be given daily over 15 minutes for 5 days on days 1 through 5.~* Azacitidine will be given 30-60 minutes before beginning the tagraxofusp infusion."

"Give intrathecally:~* 8 mg for patients age 1-1.99~* 10 mg for patients age 2-2.99~* 12 mg for patients 3-8.99 years of age~* 15 mg for patients ≥9 years of age"

"Give intrathecally:~* 30 mg for patients age 1-1.99~* 50 mg for patients age 2-2.99~* 70 mg for patients ≥3 years of age~If given as part of Triple IT Therapy:~AML Patients:~Age 1-1.99 - 24 mg Age 2-2.99 - 30 mg Age ≥3 years of age - 36 mg~AML Patients:~Age 1-1.99 - 16 mg Age 2-2.99 - 20 mg Age 3-8.99 - 24 mg Age ≥9 years of age - 30 mg"

"Given intrathecally.~AML Patients:~Age 1-1.99 - 16 mg Age 2-2.99 - 20 mg Age ≥3 years of age - 24 mg~AML Patients:~Age 1-1.99 - 8 mg Age 2-2.99 - 10 mg Age 3-8.99 - 12 mg Age ≥9 years of age - 15 mg"