Pacritinib Before Transplant for Myeloproliferative Neoplasms (MPN)

200 mg by mouth twice a day for 60 days.

Busulfan AUC of 4000 microMol-min per day providing that pharmacokinetic can be done, otherwise Busulfan dose given as a fixed dose of 100 mg/m2 daily for four days.

Questionnaires completed at baseline, 1, 3, 6, and 12 months after transplant.

Phone calls made by study staff to participant on second and third week of each month.

Allogeneic stem cell transplantation (Allo TP) 60 days after starting Pacritinib but not more than 180 days.

Fludarabine taken along with Busulfan as per standard of care as preparative regimen for allogeneic stem cell transplantation (Allo TP).