Abstract
We herein report three cases of multiple myeloma (MM), in which no M component was detected in serum or urine; however, the serum free light chain (sFLC) assay showed an excess of sFLC-κ and a high κ/λ ratio. The first case was a man in his fifties with multiple osteolytic lesions and hypercalcemia. The immunofixation of serum revealed no M component and urinary protein was below the detection level, while sFLC-κ was 10,700.0 mg/L (reference range, 3.3 to 19.4 mg/L) and the κ/λ ratio was 672.96 (reference range, 0.26 to 1.65). Although he responded to bortezomib and dexamethasone followed by high-dose melphalan with autologous hematopoietic stem cell transplantation, he relapsed with the features of plasma cell leukemia. The second case was a woman in her forties with multiple bone involvement. The immunofixation of serum and urine was negative, while sFLC-κ was 1,610.0 mg/L and the κ/λ ratio was 217.57. She was treated with bortezomib, lenalidomide, and dexamethasone. The third case was a woman in her seventies with paraplegia due to a vertebral tumor. Immunofixation was negative, sFLC-κ was 1580.0 mg/L, and the κ/ λ ratio was 141.07. Bone marrow in each case contained 63.8, 39.8, and 7.4% myeloma cells in which the κ light chain was expressed in the cytoplasm, as revealed by multicolor flow cytometry. Fluorescence in situ hybridization of myeloma cell nuclei revealed the presence of the CCND1-immunoglobulin heavy chain fusion gene (IGH) indicative of t(11;14)(q13;q32), but showed variant hybridization signal patterns. These three cases matched the criteria of recently proposed sFLC-only MM and were characterized by multiple bone involvement, the lack of significant anemia and impaired renal function, an immature myeloma cell morphology, and the CCND1-IGH fusion gene. These results support the routine use of the sFLC assay for a work-up when a patient is suspected of having a plasma cell disorder.
