Lambda Light Chain Cast Nephropathy Caused by Splenic Marginal Zone Lymphoma

We report an interesting case of an elderly male patient with splenic marginal zone lymphoma with a monoclonal cluster of differentiation (CD)5+ B cells. The patient developed signs of renal injury and was evaluated via serum protein electrophoresis and immunofixation electrophoresis, which revealed monoclonal gammopathy with elevated free lambda light chain. However, a bone biopsy ruled out a diagnosis of multiple myeloma. Upon renal biopsy, the patient was diagnosed with lambda light chain cast nephropathy. However, the patient's condition further deteriorated, and the patient eventually expired. This case highlights light chain cast nephropathy as a rare yet serious complication of lymphomas and, in particular, splenic marginal zone lymphoma.