Delayed Onset Tumor Lysis Syndrome after Initial Pomalidomide Treatment in a Patient with Refractory Multiple Myeloma

An 82-year-old male with multiple myeloma developed tumor lysis syndrome (TLS) 9 days after initial pomalidomide and dexamethasone treatment (PomD). His prior therapy included melphalan and prednisolone; bortezomib and dexamethasone; and lenalidomide and dexamethasone without any TLS symptoms. PomD was administered due to myeloma progression, and his renal function improved gradually without acute adverse effects. However, on day 9, his renal function suddenly worsened, and serum lactate dehydrogenase, uric acid, potassium, and phosphorous levels were elevated. There were no symptoms of infection, or remarkable changes in urinary findings. After PomD was discontinued and hydration was started on the same day, his renal function improved immediately, and treatment was resumed on day 24. TLS is a relatively rare, but life-threatening, complication in multiple myeloma patients and this onset period is sometimes quite different from other hematological malignancies. In addition to myelosuppression, TLS is a critical adverse event of PomD that may have delayed onset.