Pembrolizumab and Radiation Therapy in Patients With Relapsed or Refractory Multiple Myeloma

Inclusion Criteria: * International Staging System (ISS) stage I-III multiple myeloma that has progressive, relapsed, or refractory disease * Able to give informed consent * Eastern Cooperative Oncology Group (ECOG) 0-1 * Relapsed and/or refractory myeloma; there is no minimum or maximum number of previous therapies that a patient may have received previously before being put on the current trial * ≥ 1 osseous and/or extra-osseous lesion that can be radiated * Candidate for pembrolizumab (as determined by physician, and adequate organ function) * Candidate for radiotherapy (as determined by treatment physician); these patients can have symptomatic disease and/or asymptomatic disease; a minimum of one site of radiation is required to any osseous and/or any extra-osseous disease; radiation to any bony parts of the head and neck, skull, spine, ribs, and/or extremities are allowed; radiation to any bony part for documented lytic disease is allowed; radiation to any soft tissue plasmacytoma (including osseous and extra-osseous plasmacytoma) is allowed; the only exclusion criteria for radiation, is central nervous system (CNS) metastases * Measurable myeloma disease (urine protein \> 200 mg in 24 hours \[hr\] urine collection, serum free light chain ratio \> 100 with an abnormal k/l ratio, serum M protein \> 0.5 g/dl); 12 of the 24 patients do not have to have measurable disease * Negative urine pregnancy test within 2 weeks for female subjects; female subjects of childbearing pot…