Tagraxofusp in Treating Patients With Blastic Plasmacytoid Dendritic Cell Neoplasm After Stem Cell Transplant

Inclusion Criteria: * Eligible patients will be aged \>= 18 years. Pediatric patients age 2 years and older will be considered on a case by case basis. * Diagnosis of blastic plasmacytoid dendritic cell neoplasm (BPDCN) according to World Health Organization (WHO) classification or confirmed by hematopathology * The patients must be in partial response or better * \> 30 days post-transplant without active or chronic infections * Karnofsky performance status \>= 60%; Lansky \>= 60 * Left ventricular ejection fraction (LVEF) \>= institutional lower limit of normal by multigated acquisition (MUGA) scan or echocardiogram within 30 days of first protocol treatment * Diffusion capacity of the lung for carbon monoxide (DLCO) \> 40% of predicted value (corrected for hemoglobin) within 3 months of registration * Forced expiratory volume in 1 second (FEV1) \> 40% of predicted value within 3 months of registration * Forced vital capacity (FVC) \> 40% of predicted value within 3 months of registration * Serum creatinine =\< 1.5 mg/dL (133 mmol/L) * Serum albumin \>= 3.2 g/dL (or \>= 32 g/L) without IV albumin within the previous 72 hours * Bilirubin =\< 1.5 x the upper limit of normal (\[ULN\] except patients with Gilbert syndrome in whom bilirubin level of \> 1.5 x ULN will be allowed) * Aspartate aminotransferase (AST) and alanine aminotransferase (ALT) =\< 2.5 times ULN * Hemoglobin \>= 8 g/dL with or without transfusion in the last 7 days * Absolute neutrophil count (ANC) \>= 1000 w…