Pembrolizumab in Treating Patients With Intermediate or High-Risk Smoldering Multiple Myeloma

PRIMARY OBJECTIVE: I. To determine the overall response rate after 8 cycles of treatment according to the International Myeloma Working Group Criteria (IMWG). SECONDARY OBJECTIVES: I. To determine time to progression to multiple myeloma (TTP) at 30 months from study entry. II. To determine overall survival (OS). III. To determine duration of response (DOR). IV. To determine the clinical benefit rate (CBR) after 8 cycles of treatment according to the modified IMWG Criteria for multiple myeloma (MM). V. To evaluate safety and tolerability of single agent treatment in this population. EXPLORATORY OBJECTIVES: I. Rate of minimal residual disease (MRD) negativity at complete remission (CR). II. Molecular profiling (including whole exome sequencing and gene expression profiling) and cellular (including flow cytometry) profiling at baseline and/or at progression using bone marrow aspirate samples and peripheral blood. III. Immunophenotypic characterization of dendritic, T-, B-, natural killer (NK)- and natural killer T (NKT)-cells, and inhibitory/activation markers on tumor cells at baseline and at completion of 8 cycles of therapy in bone marrow aspirate samples and/or peripheral blood. IV. Evaluation of changes in PD-L1 and PD-1 expression at baseline/end of 8 cycles of treatment and correlate with clinical response. OUTLINE: Patients receive pembrolizumab intravenously (IV) over 30 minutes on day 1. Treatment repeats every 21 days for up to 24 courses in the absence of disease progression or unacceptable toxicity. After completion of study treatment, patients are followed up every 6-12 months.