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

Inclusion Criteria: * Adult patients with intermediate or high-risk smoldering multiple myeloma (SMM) are eligible; patients need to have clonal bone marrow plasma cells \>= 10% and/or monoclonal spike in blood of \>= 3 g/dL and/or monoclonal urine component (Bence jones proteinuria) \>= 500 mg/24 hours and need to meet subject inclusion criteria and exclusion criteria as per below * Patients must have histologically confirmed SMM based on the following criteria: * (A) Mayo clinic criteria (patient must have at least 2 risk factors present): * 1\. Bone marrow core biopsy plasma cell involvement by cluster of differentiation (CD)138 immunohistochemistry \>= 10% * 2\. Monoclonal spike \>= 3 g/dL * 3\. Free light chain ratio in serum \< 0.125 or \> 8; \*2 of 3 risk factors: intermediate risk for progression at a rate of 51% at 5 years, \*3 of 3 risk factors: high risk for progression at a rate of 76% at 5 years * OR (B) Programa para el Tratamiento de Hemopatias Malignas (PETHEMA) criteria (patient must have at least 1 risk factor present) * 1\. \>= 95% abnormal plasma cells/total plasma cells in bone marrow compartment * 2\. Immunoparesis \*1 of 2 risk factors: intermediate risk for progression at a rate of 46% at 5 years, \*2 of 2 risk factors: high risk for progression at a rate of 72% at 5 years * OR (C) Southwestern Oncology Group (SWOG) criteria (patient must have 2 risk factors present or one risk factor if this risk factor is a 70-gene signa…