A Study for Participants Who Participated in Prior Clinical Studies of ASTX727 (Standard Dose)

Inclusion Criteria

• Inclusion Criteria for the Main Extension Study: Participants must fulfill all of the following inclusion criteria: 1. Previous participation in a Taiho (formerly Astex)-sponsored ASTX727 clinical trial (including, but not limited to studies ASTX727-01, ASTX727-02, and ASTX727-04, , ASTX727-17, and ASTX727-18, and the food effect substudy of ASTX727-06) in which the participant was treated with ASTX727 and was still on active treatment with ASTX727 at the time of study completion as determined by Taiho. 2. Participant is considered to be benefitting from ASTX727 treatment in the opinion of the treating investigator at the time of parent study completion (Participants must not be withdrawn from the parent study until eligibility for this study is confirmed). 3. Participant is able to understand and comply with the study procedures and understands the risks involved in the study. 4. Participant provides legally effective informed consent before undergoing any study-specific procedure. 5. Women of childbearing potential must not be pregnant or breastfeeding and must have a negative pregnancy test at screening. Women of childbearing potential must agree to practice 1 highly effective contraceptive methods of birth control during the study and for 6 months after the last dose of study treatment, agree not to donate eggs for the purpose of reproduction during this period and must agree not to become pregnant for 6 months after completing treatment; men with female partners of childbearing potential must agree to practice 2 highly effective contraceptive measures and must agree not to father a child while receiving ASTX727 and for at least 3 months after completing ASTX727 treatment. Inclusion Criteria for the Food Effect Substudy: 1. Participants must have a confirmed diagnosis of- i. Myelodysplastic syndromes (MDS) including all French-American-British subtypes (refractory anemia, refractory anemia with ringed sideroblasts, refractory anemia with excess blasts, refractory anemia with excess blasts in transformation, chronic myelomonocytic leukemia [CMML])), and participants with MDS International Prognostic Scoring System (IPSS) int-1, int-2, or high-risk MD. ii. Acute myeloid leukemia (AML), as diagnosed according to the 2016 World Health Organization (WHO) guidelines on acute leukemia, of any subtype except M3 (acute promyelocytic leukemia), who are not candidates for intensive chemotherapy, including participants receiving hypomethylating agent (HMA) treatment, who have a confirmed diagnosis and a prior confirmatory bone marrow report. Participants who are currently receiving HMA treatment must complete the ongoing (at the time of Screening) treatment cycle before enrolling in this study; timing of start of treatment cycle with ASTX727 is at the principal investigator's discretion. 2. Eastern Cooperative Oncology Group (ECOG) performance status of 0 to 2. 3. Adequate organ function defined as follows: 1. Hepatic: Total bilirubin ≤1.5 × upper limit of normal (ULN); aspartate aminotransferase/serum glutamic-oxaloacetic transaminase (AST/SGOT) and alanine aminotransferase/serum glutamic-pyruvic transaminase (ALT/SGPT) ≤5 × ULN. 2. Renal: Calculated creatinine clearance ≥60 mL/min. Exclusion Criterion for the Main Extension Study: 1. Any participant who, in the opinion of the investigator, may have other conditions, organ dysfunction, or for whom safety data from parent study participation suggests the risks of continuing treatment with ASTX727 may outweigh the benefits. Exclusion Criteria for the Food Effect Substudy: 1. Participants with known or suspected hypersensitivity to decitabine, cedazuridine, or any of the excipients in the ASTX727 tablets. 2. Poor medical risk because of other conditions such as uncontrolled systemic diseases or active uncontrolled infections. 3. Life-threatening illness, medical condition or organ system dysfunction, or other reasons including laboratory abnormalities, which, in the Investigator's opinion, could compromise the participant's safety, interfere with the absorption or metabolism of decitabine + cedazuridine or compromise the integrity of the study outcomes. 4. Prior gastric surgery for ulcer disease, weight loss, etc, that would impair normal motility or absorption. 5. Second malignancy currently requiring active chemotherapy. To clarify, participants with breast or prostate cancer stable on or responding to endocrine therapy, are eligible. 6. Known history of human immunodeficiency virus or known seropositive for hepatitis C virus or hepatitis B virus. 7. Active uncontrolled gastric or duodenal ulcer. 8. Participants with acute promyelocytic leukemia. 9. Prior cytotoxic chemotherapy for AML except for hydroxyurea to control high white blood cell (WBC) counts. 10. Treated with any investigational drug or therapy within 2 weeks of study treatment, or 5 half-lives, whichever is longer, before the protocol-defined first dose of study treatment, or ongoing clinically significant AEs from previous treatment with investigational drug or therapy.