This is a multi-center, non-randomized and open-label phase I/IIa clinical study to evaluate the safety, tolerability, and efficacy of ICP-490 in patients with relapsed and/or refractory multiple myeloma.

Inclusion Criteria:

1. Aged ≥ 18 years old.
2. Diagnosed as relapsed and/or refractory multiple myeloma .The patient must have measurable diseases.Eastern Cooperative Oncology Group (ECOG) Performance Status (PS) score of 0-2.
3. Patients must have adequate organ function. Expected survival time ≥ 6 months.
4. All toxicities caused by prior anticancer therapy must have recovered to Grade ≤ 1 (based on CTCAE v5.0) except alopecia and fatigue.

Female patients of childbearing potential should have a negative blood pregnancy test result within 48 h prior to the first dose of investigational drug.

Exclusion Criteria:

1. Known active central nervous system (CNS) involvement or history of the disease, or clinical signs of multiple myeloma meningeal/spinal meningeal involvement.

2. Patients with solitary plasmacytoma; plasma cell leukemia (PCL) (active PCL or history of PCL); Waldenström's macroglobulinemia; POEMS syndrome or symptomatic amyloidosis.

3. Prior active or history of malignancies other than MM, occurring within 5 years prior to the first dose of investigational drug, with the exception of radically treated local curable cancers.

4. Uncontrolled or severe cardiovascular disorders.

5. Any active infection within 14 days prior to the first dose of investigational drug.

6. Patients with diseases restricted from participation as described in the protocol

7. Having undergone major surgery within 28 days prior to the first dose of investigational drug, or minor surgery within 2 weeks prior to the first dose. Any severe or uncontrolled systemic disease evaluated by investigatorthat may increase the risk associated with study participation and drug administration or affect the patient's ability to receive the investigational drug.

8. Patients who have received any other systemic treatment, anti-tumor traditional Chinese (herbal) medicine therapy , and any other investigational drug therapy for MM within 28 days or 5 half-lives of the drugs (whichever is shorter) prior to the first dose of investigational drug.

9. Patients who have received systemic treatment with corticosteroids or other immunosuppressive drugs within 14 days prior to the first dose of investigational drug.

   Subjects are allowed to use topical, ocular, intra-articular, intranasal, and inhaledcorticosteroid ; short-term use (≤ 7 days) of corticosteroid for prophylaxis (e.g., contrast agent allergy) or for the treatment of non-autoimmune diseases (e.g., delayed hypersensitivity reaction caused by contact allergens) is permitted.

10. Patients who have received medications or foods with strong inhibitory or inductive effects on cytochrome P450 CYP3A, and proton pump inhibitorswithin 2 weeks prior to the first dose of investigational drug, or are planning to receive them during the study.

11. Patients with a history of severe allergic reactions to IMIDs , or dexamethasone, or to any component contained in ICP-490 or dexamethasone formulation (CTCAE V5.0 Grade > 3).