Long-term follow-up of patients with monoclonal gammopathy of undetermined significance after kidney transplantation

Introduction: Long-term data regarding kidney transplantation (KTx) patients with monoclonal gammopathy of undetermined significance (MGUS) are scarce. We evaluated the long-term outcomes of these patients in a single-center retrospective study from the Mayo Clinic, Rochester, Minn., USA. Methods: Patients who had an MGUS before transplant or developed one after KTx were selected. Monoclonal protein was screened as part of the KTx evaluation by serum protein electrophoresis. Screening for posttransplant lymphoproliferative disorder (PTLD) or MGUS after transplant was not required by protocol. Patients with multiple myeloma, dysproteinemia-related kidney disease or no pretransplant serum protein electrophoresis were excluded. Results: Between 1963 and 2006, 3,518 patients underwent KTx. MGUS was identified in 42 patients, with 23 before transplant and 19 after transplant. Median follow-up for these patients was 8.5 years (range 0.3-37). Four (17.4%) pretransplant MGUS patients developed a hematologic malignancy: 2 smoldering multiple myeloma and 2 PTLD - an Epstein-Barr virus-positive diffuse large cell lymphoma and a Hodgkin lymphoma. None of the 19 patients who developed an MGUS after transplant progressed to multiple myeloma, but 2 (10.5%) developed Epstein-Barr virus-negative T cell lymphoproliferative disorders at 16 and 26 years after transplant. Median survival was 26.1 and 28.0 years for the pretransplant and posttransplant MGUS groups, respectively. Conclusion: Progression from true MGUS to multiple myeloma is rare after KTx. KTx appears safe in true MGUS patients if the monoclonal gammopathy was not the cause of the kidney disease. None of the patients progressed to multiple myeloma, but 2 developed smoldering multiple myeloma and several developed PTLD. Further studies are needed to explain the relationship between MGUS and PTLD.