Participants received oprozomib 210 mg once daily on days 1, 2, 8, 9, 15, 16, 22, and 23 (2/7 schedule) of each 28-day treatment cycle, in combination with lenalidomide 25 mg on days 1 through 21 and dexamethasone 20 mg/day on days 1, 2, 8, 9, 15, 16, 22, and 23, until progression of disease, unacceptable toxicity, or for 24 cycles, whichever occurred first. After completing 24 cycles of treatment, participants with stable disease or better could have continued on oprozomib with or without dexamethasone pretreatment.

Participants received oprozomib 240 mg once daily on days 1, 2, 8, 9, 15, 16, 22, and 23 (2/7 schedule) of each 28-day treatment cycle, in combination with lenalidomide 25 mg on days 1 through 21 and dexamethasone 20 mg/day on days 1, 2, 8, 9, 15, 16, 22, and 23, until progression of disease, unacceptable toxicity, or for 24 cycles, whichever occurred first. After completing 24 cycles of treatment, participants with stable disease or better could have continued on oprozomib with or without dexamethasone pretreatment.

Participants received oprozomib 210 mg once daily on days 1, 2, 8, 9, 15, 16, 22, and 23 (2/7 schedule) of each 28-day treatment cycle, in combination with oral cyclophosphamide 300 mg/m² on days 1, 8, and 15 and dexamethasone 20 mg/day on days 1, 2, 8, 9, 15, 16, 22, and 23, until progression of disease, unacceptable toxicity, or for 8 cycles, whichever occurred first. After completing 8 cycles of treatment, participants with stable disease or better were to continue on oprozomib with dexamethasone premedication for a total of 24 cycles or until progression of disease or unacceptable toxicity. After completing 24 cycles of treatment, participants without evidence of disease progression could have continued on oprozomib with or without dexamethasone pretreatment.

Administered orally at a dose of 25 mg on days 1 through 21 of each 28-day cycle for a maximum of 24 cycles.

Administered at 20 mg, orally, on days 1, 2, 8, 9, 15, 16, 22, and 23 of each 28-day cycle. After the first cycle the dose may be decreased to 10 mg/day in participants > 75 years of age, at the discretion of the investigator.

Administered orally at 300 mg/m² (up to a maximum of 600 mg) on days 1, 8, and 15 of each 28-day cycle for a maximum of 8 cycles of therapy (approximately 8 months).

ORR is defined as the percentage of participants with a best overall response of partial response (PR), very good PR (VGPR), complete response (CR), or stringent CR (sCR) based on the International Myeloma Working Group Uniform Response Criteria.

PR: ≥ 50% reduction of serum M-protein and ≥ 90% reduction in urine M-protein or to < 200 mg/24 hrs, or a ≥ 50% decrease in dFLC. A ≥ 50% decrease in the size of soft tissue plasmacytomas present at baseline.

VGPR: Serum and urine M-protein detectable by immunofixation but not electrophoresis or ≥ 90% decrease in serum M-protein with urine M-protein <100 mg/24 hrs. If disease measurable only by SFLC, ≥ 90% decrease in the difference between involved and uninvolved FLC levels (dFLC).

CR: No immunofixation on serum and urine, disappearance of soft tissue plasmacytomas and <5% plasma cells in BM. Normal serum free light chain (SFLC) ratio if disease measurable only by SFLC.

sCR: As for CR, and absence of clonal plasma cells in bone marrow (BM).

Duration of response was defined as the time from first evidence of partial response (PR) or better to confirmation of disease progression or death due to any cause.

Median DOR was estimated using Kaplan-Meier methods. Participants who started a new anticancer therapy before documentation of disease progression or death, or who were alive without documentation of disease progression before the data cut-off date or who died or had disease progression immediately after more than 1 consecutively missed disease assessment visit were censored at the date of last disease assessment.

Progression-free survival is defined as the time from the start of treatment to disease progression or death (due to any cause), whichever occurred first. Median PFS was estimated using Kaplan-Meier methods. Participants who started a new anticancer therapy before documentation of disease progression or death, or who were alive without documentation of disease progression before the data cut-off date or who died or had disease progression immediately after more than 1 consecutively missed disease assessment visit were censored at the date of last disease assessment.

Participants received oprozomib 180 mg once daily on days 1 to 5 and days 15 to 19 (5/14 schedule) of each 28-day treatment cycle, in combination with lenalidomide 25 mg on days 1 through 21 and dexamethasone 20 mg/day on days 1, 2, 8, 9, 15, 16, 22, and 23, until progression of disease, unacceptable toxicity, or for 24 cycles, whichever occurred first.

After completing 24 cycles of treatment, participants with stable disease or better could have continued on oprozomib with or without dexamethasone pretreatment.

Participants received oprozomib 210 mg once daily on days 1 to 5 and days 15 to 19 (5/14 schedule) of each 28-day treatment cycle, in combination with lenalidomide 25 mg on days 1 through 21 and dexamethasone 20 mg/day on days 1, 2, 8, 9, 15, 16, 22, and 23, until progression of disease, unacceptable toxicity, or for 24 cycles, whichever occurred first.

Participants received oprozomib 210 mg once daily on days 1, 2, 8, 9, 15, 16, 22, and 23 (2/7 schedule) of each 28-day treatment cycle, in combination with lenalidomide 25 mg on days 1 through 21 and dexamethasone 20 mg/day on days 1, 2, 8, 9, 15, 16, 22, and 23, until progression of disease, unacceptable toxicity, or for 24 cycles, whichever occurred first.

After completing 24 cycles of treatment, participants with stable disease or better could have continued on oprozomib with or without dexamethasone pretreatment.

Participants received oprozomib 240 mg once daily on days 1, 2, 8, 9, 15, 16, 22, and 23 (2/7 schedule) of each 28-day treatment cycle, in combination with lenalidomide 25 mg on days 1 through 21 and dexamethasone 20 mg/day on days 1, 2, 8, 9, 15, 16, 22, and 23, until progression of disease, unacceptable toxicity, or for 24 cycles, whichever occurred first.

After completing 24 cycles of treatment, participants with stable disease or better could have continued on oprozomib with or without dexamethasone pretreatment.

Participants received oprozomib 210 mg once daily on days 1, 2, 8, 9, 15, 16, 22, and 23 (2/7 schedule) of each 28-day treatment cycle, in combination with oral cyclophosphamide 300 mg/m² on days 1, 8, and 15 and dexamethasone 20 mg/day on days 1, 2, 8, 9, 15, 16, 22, and 23, until progression of disease, unacceptable toxicity, or for 8 cycles, whichever occurred first.

After completing 8 cycles of treatment, participants with stable disease or better were to continue on oprozomib with dexamethasone premedication for a total of 24 cycles or until progression of disease or unacceptable toxicity. After completing 24 cycles of treatment, participants without evidence of disease progression could have continued on oprozomib with or without dexamethasone pretreatment.