A New IgG-λ Band during Therapy in Light-Chain Myeloma

A 66-year-old male with a history of renal cell carcinoma presented to the local hospital for rib pain. Physical examination of the patient was unremarkable. A follow-up chest computed tomography (CT) exam revealed the presence of multiple lytic lesions on the ribs, sternum, and clavicles. Due to his previous cancer history, these findings suggested bone metastases. Additional investigation included a CT-guided biopsy of the posterior left eighth rib that disclosed an increased number of monotypic lambda plasma cells, a finding that prompted additional investigations. Laboratory workup with serum protein electrophoresis (SPEP) revealed hypogammaglobulinemia, confirmed with decreased serum IgM (19 mg/dL; reference interval [RI] 37 to 286 mg/dL], IgG (644 mg/dL; RI 767 to 1590 mg/dL) and IgA (35 mg/dL; RI 61 to356 mg/dL). Serum immunofixation (IFE) demonstrated a small λ M-protein in the beta fraction without an associated heavy chain (no IgG, IgA, IgM, IgD, or IgE observed), consistent with a lambda light chain–restricted pattern. Proteinuria was observed (28 828 mg/24 h; RI