Olutasidenib for the Treatment of Patients With IDH1 Mutated AML, MDS or CMML After Donor Hematopoietic Cell Transplant

Inclusion Criteria:

* Documented informed consent of the participant and/or legally authorized representative
* Agreement to allow the use of archival tissue from diagnostic tumor biopsies. If unavailable, exceptions may be granted with study principal investigator (PI) approval
* Age: ≥ 18 years
* Eastern Cooperative Oncology Group (ECOG) ≤ 2 or Karnofsky performance status (KPS) ≥ 70
* Patients who are scheduled to receive or have already undergone allogeneic hematopoietic cell transplantation (alloHCT) from any donor type, any conditioning regimen, and regardless of GVHD prophylaxis will be include
* Patients must have AML, MDS, or CMML with mIDH1 diagnosis at diagnosis (regardless of time from HCT). Note: Patient with pre-HCT disease relapse will no be included if mIDH1 is not detected after relapse
* Day 30 marrow post alloHCT should show evidence of morphologic remission with \< 5% bone marrow (BM) blasts. Patients with MRD-positive status either by flow cytometry or IDH1 mutation testing will be eligible
* Patients with previous therapy with IDH1 inhibitors will be included
* Absolute neutrophil count (ANC) \> 1000/mm\^3 (within 28 days prior to day 1 of protocol)
* Hemoglobin ≥ 8.0 gm/dL (within 28 days prior to day 1 of protocol)
* Platelets ≥ 50,000/mm\^3 (within 28 days prior to day 1 of protocol) Note: Patients with lower counts can enroll if infection cytomegalovirus (CMV)/human herpes virus 6 (HHV6), etc. is being treated actively
* Bilirubin ≤ 2 x upper limit of normal (ULN) (within 28 days prior to day 1 of protocol) (unless has Gilbert's disease). Patients with abnormal liver function tests (LFTs) due to active GVHD will not be eligible
* Aspartate aminotransferase (AST) (serum glutamic oxaloacetic transaminase \[SGOT\])/alanine aminotransferase (ALT) (serum glutamic pyruvic transaminase \[SGPT\]) ≤ 2 x ULN (within 28 days prior to day 1 of protocol). Patients with abnormal LFTs due to active GVHD will not be eligible
* Creatinine clearance of ≥ 30/min/1.73 m\^2 for participants with creatinine levels above institutional normal per 24 hour urine test or the Cockcroft-Gault formula (within 28 days prior to day 1 of protocol)
* Corrected QT interval (QTc) ≤ 480 ms (Note: To be performed within 28 days prior to day 1 of protocol therapy)
* Seronegative for HIV antigen/antibody (Ag/Ab) combo, hepatitis C virus (HCV) (if positive, hepatitis C ribonucleic acid \[RNA\] quantitation must be performed), active hepatitis B virus (HBV) (surface antigen negative), and syphilis (rapid plasma reagin \[RPR\]) (within 28 days prior to day 1 of protocol)
* Women of childbearing potential (WOCBP): negative urine or serum pregnancy test (within 28 days prior to day 1 of protocol). If the urine test is positive or cannot be confirmed as negative, a serum pregnancy test will be required
* Agreement by females and males of childbearing potential, defined as not being surgically sterilized (men and women) or have not been free from menses for \> 1 year (women only), to use an effective method of birth control or abstain from heterosexual activity for the course of the study through at least 3 months after the last dose of protocol therapy

Exclusion Criteria:

* Patients with more than one allogeneic HCT
* History of allergic reactions attributed to compounds of similar chemical or biological composition to study agent
* Active diarrhea considered clinically significant and may impair oral drug administration
* Clinically significant uncontrolled illness
* Uncontrolled infection requiring systemic antimicrobials

  * Active infection: Patients with treated viral, bacterial or fungal infections that are controlled on therapy will be allowed to participate
* Participant has detectable human immunodeficiency virus (HIV) viral load within the previous 6 months (must have viral load testing prior to study enrollment if participant has a known history of HIV 1/2 antibodies)
* Active hepatitis B or C, or HIV
* Other active malignancy. Participants with history of prior malignancy treated with curative intent who achieved CR more than 2 years before study entry are eligible. This exclusion rule does not apply to non-melanoma skin tumors and in-situ cervical cancer
* Females only: Pregnant or breastfeeding
* Active grade II-IV acute GVHD per Mount Sinai Acute Graft Versus Host Disease International Consortium (MAGIC) criteria and/or requiring systemic steroids with prednisone dose equivalent of ≥ 0.25 mg/kg at end of 4 weeks. Patients with a mild form of acute GVHD involving skin, gut or liver requiring topical steroid creams or oral beclomethasone (8 mg/day), entocort, (9 mg/day) and/or solumedrol (and equivalent prednisone) will be allowed
* Any other condition that would, in the investigator's judgment, contraindicate the patient's participation in the clinical study due to safety concerns with clinical study procedures
* Prospective participants who, in the opinion of the investigator, may not be able to comply with all study procedures (including compliance issues related to feasibility/logistics)