The ORR is defined as percentage of participants who achieve a best response of stringent complete response (sCR), complete response (CR), very good partial response (VGPR), or partial response (PR) during the study. sCR: negative immunofixation in serum and urine; disappearance of any soft tissue plasmacytomas; \< 5% plasma cells in bone marrow; normal free light chain (FLC) ratio; and absence of clonal cells in bone marrow. CR: negative immunofixation in serum and urine; disappearance of any soft tissue plasmacytomas; and \<5% plasma cells in bone marrow. VGPR: serum and urine M-protein detectable by immunofixation but not on electrophoresis; 90% or greater reduction in serum M-protein level and urine M-protein level less than 100 milligrams (mg)/24 hours. PR: ≥50% reduction in serum M-protein level; ≥90% reduction in 24-hour urinary M-protein level or reduction to less than 200 mg per 24 hours; and ≥50% reduction in the size of any soft tissue plasmacytomas present at baseline.

MTD was based on the assessment of dose-limiting toxicity (DLT) during cycle 1 only and was defined as the highest dose at which fewer than one-third of participants in a cohort experience DLT. A DLT was defined as any of the following drug-related toxicities occurring during Cycle 1: Hematologic adverse events (AEs) (Grade 4 hematologic AEs, Grade 3 hematologic AEs with sequelae); Grade 3 nonhematologic AEs; Neuropathy (Grade 2 neuropathy, Grade 1 neuropathy with pain, worsening grade of neuropathy or new symptoms of pain associated with neuropathy); Any other toxicity that, in the judgment of the principal investigator, was a DLT; If a participant cannot receive 75% of the planned dose for any of the 3 agents (missing \>1 dose of CEP-18770, or \>5 doses of lenalidomide, or \>1 dose of dexamethasone \[either consecutively or separately\]), due to a drug-related AE, the event was considered a DLT, even if the grade of toxicity was lower than specified DLT determination as described above.