A Study for Oral SY-2101 for Participants With Acute Promyelocytic Leukemia

Key Inclusion Criteria:

* Participants must have a diagnosis of APL characterized by the presence of the t(15;17) translocation or PML/RARA gene expression via reverse transcription polymerase chain reaction (RT-PCR), fluorescence in situ hybridization (FISH), or cytogenetics. Participants with low-risk APL may be eligible for all parts of this study; participants with high-risk APL are only eligible for the single-dose modules if they have completed a treatment regimen that included ATO within 6 months prior to the Screening Visit.
* Participants must have received ATO plus ATRA induction therapy and must have received or be eligible and planning to receive consolidation therapy with ATO plus ATRA in alignment with National Comprehensive Cancer Network (NCCN) guidelines for low-risk APL prior to their enrollment in the study; or participants must have completed a treatment regimen that included ATO within 6 months prior to the Screening Visit.
* Participants must be able to tolerate full dose ATO per NCCN guidelines.
* Participants must be in morphological complete remission (CR) at the end of induction.
* Participants must have a serum or high-sensitivity urine pregnancy test (for females of childbearing potential) that is negative at the Screening Visit and immediately prior to initiation of study treatment (first dose of study drug).

Key Exclusion Criteria:

* Participants who have demonstrated relapse and therefore are not eligible for further consolidation.
* Participants currently receiving treatment for a non-APL malignancy (not including basal cell carcinoma, non-melanoma skin cancer, cervical carcinoma in situ, or localized prostate cancer treated with hormone therapy). Participants with history of other cancers should be free of disease for at least 2 years prior to the Screening Visit.
* Participants with an active, life-threatening, or clinically-significant uncontrolled systemic infection requiring hospitalization.
* Immunocompromised participants with increased risk of opportunistic infections, including known human immunodeficiency virus (HIV)-positive participants with cluster of differentiation 4 (CD4) counts ≤350 cells/millimeters (mm\^3) or history of opportunistic infection in the last 12 months.
* Participants with a known active or chronic hepatitis B or active hepatitis C virus (HCV) infection. Participants with a history of HCV infection who have completed curative therapy for HCV at least 12 weeks before the Screening Visit and have a documented undetectable viral load at the Screening Visit are eligible for enrollment.
* Participants who have not adequately recovered from a major surgery within 4 weeks of starting study drug administration.
* Participants who received any other investigational agents within 4 weeks of the Screening Visit or \<5 half-lives since completion of previous investigational therapy have elapsed, whichever is shorter.
* Participants who have a hypersensitivity to arsenic.
* Participants who have experienced the following Grade ≥3 non-hematologic toxicities associated with ATO administration: QT prolongation, hepatotoxicity, neurotoxicity, cardiac function abnormalities. Participants who experienced other severe and life-threatening clinically-significant ATO-related AEs that are considered, in the judgement of the investigator, to increase participant risk with continued ATO treatment are also excluded.

Other inclusion/exclusion criteria may apply.