To Assess the Safety and Tolerability of INCB000928 in Participants With Myelodysplastic Syndromes or Multiple Myeloma.

Inclusion Criteria:

Agreement to avoid pregnancy or fathering children.
Participants who are transfusion-dependent or present with symptomatic anemia

For MDS participants:

Ineligible to receive or have not responded to available therapies for anemia such as ESAs or lenalidomide.
Not requiring cytoreductive therapy other than hydroxyurea.
BM and peripheral blood myeloblast count < 10%.
Histologically confirmed diagnosis of the MDS, CMML and unclassifiable MDS/MPN overlap syndromes.

For MM participants:

Histologically confirmed diagnosis of MM.
After failure of available standard treatments such as alkylating agents, glucocorticoids, immunomodulatory drugs (lenalidomide,pomalidomide, or thalidomide), proteasome inhibitors (bortezomib or carfilzomib), and daratumumab.

Exclusion Criteria:

Any prior allogeneic stem cell transplantation or a candidate for such transplantation.
Any major surgery within 28 days before the first dose of study drug.
Any prior chemotherapy, immunomodulatory drug therapy, immunosuppressive therapy, biological therapy, endocrine therapy, targeted therapy, or antibody or hypomethylating agent to treat the participant's disease within 5 half-lives or 28 days (whichever is shorter) before the first dose of study drug.
Undergoing treatment with another investigational medication or having been treated with an investigational medication within 28 days before the first dose of study drug. -Undergoing treatment with ESAs, granulocyte colony-stimulating factor or granulocyte/macrophage colony-stimulating factor, romiplostin, or eltrombopag at any time within 28 days before the first dose of study drug.
Undergoing treatment with a strong or potent inhibitor or inducer of CYP3A4/5 within 28 days or 5 half-lives (whichever is longer) before the first dose of study drug or expected to receive such treatment during the study.
History of clinically significant or uncontrolled cardiac disease.
History or presence of an abnormal ECG that, in the investigator's opinion, is clinically Meaningful.
Presence of chronic or current active infectious disease requiring systemic antibiotic, antifungal, or antiviral treatment.
Diagnosis of chronic liver disease.