RecruitingDrug trialPre-emptive Therapy With DEC-C to Improve Outcomes in MDS Patients With Measurable Residual Disease Post Allogeneic Hematopoietic Cell TransplantThe investigators hypothesize that early measurable residual disease (MRD)-guided pre-emptive therapy with decitabine + cedazaridine (DEC-C) will decrease the risk of progression in post-transplant myelodysplastic syndromes (MDS) patients with persistent mutations (molecular MRD). To detect molecular MRD, the investigators will perform ultra-deep, error-corrected panel-based sequencing (MyeloSeq-HD) at Day 30 in post-transplant MDS patients. The investigators will treat patients with detectable molecular MRD with DEC-C to determine if pre-emptive, MRD-guided therapy with DEC-C decreases relapse rates and improves progression-free survival.