To Evaluate Safety, Tolerability, and Clinical Activity of the Antibody-drug Conjugate, GSK2857916 Administered in Combination With Lenalidomide Plus Dexamethasone (Arm A), or in Combination With Bortezomib Plus Dexamethasone (Arm B) in Participants With Relapsed/Refractory Multiple Myeloma (RRMM)

Study Summary

This study will evaluate the safety and tolerability profile of belantamab mafodotin when administered in combination with approved regimens of either Lenalidomide Plus Dexamethasone \[Len/Dex (Treatment A)\] or Bortezomib Plus Dexamethasone \[Bor/Dex (Treatment B)\] in participants with RRMM, i.e., those who have relapsed or who are refractory to at least 1 line of approved therapy. Participants receiving treatment A, may continue combination treatment until the occurrence of progressive disease (PD), intolerable adverse events (AEs ), consent withdrawal, death or end of study. The participants receiving treatment B, may continue combination treatment for a total of up to 8 cycles. After 8 cycles of combination therapy, the participants will continue treatment with belantamab mafodotin, as a monotherapy until the occurrence of PD, intolerable AEs, consent withdrawal, death or end of study.

Primary Outcome

DLT is an adverse event (AE) that is considered by the investigator to be clinically relevant and attributed to the study therapy during the 28 day DLT period and meets at least one of the DLT criteria: Grade 3 or greater febrile neutropenia lasting \>48 hours (h) despite adequate treatment; Grade 4 thrombocytopenia \<25,000/mm\^3 accompanied by significant bleeding; any Grade 3 or greater non-hematologic laboratory value (if laboratory abnormality persist \>48 h despite supportive treatment or

Interventions

• DRUG Belantamab mafodotin
• DRUG Dexamethasone
• DRUG Lenalidomide
• DRUG Bortezomib