Lymphoplasmacytic lymphoma with IgG-λ and free λ light chain paraprotein: A case report.

RATIONALE: Lymphoplasmacytic lymphoma (LPL) represents a rare, indolent form of B-cell neoplasm, with non-immunoglobulin M subtypes, including the immunoglobulin G (IgG)-λ variant, being notably uncommon. In this report, we document a case of LPL distinguished by the presence of monoclonal IgG-λ immunoglobulin and free λ light chains, alongside its distinctive molecular characteristics and therapeutic outcomes.

PATIENT CONCERNS: A 58-year-old male presented with fatigue, leukocytosis (75.45 × 109/L, 88.8% lymphocytes), lymphadenopathy, and splenomegaly. Serum studies detected an IgG-λ monoclonal protein (6.74 g/L) with concurrent elevation of free λ light chains. Bone marrow biopsy revealed marked hypercellularity, with lymphocytes comprising 80% of nucleated cells (predominantly plasmacytoid lymphocytes) and 5% plasma cell clusters. Genetic testing identified mutations in MYD88, CXCR4, and IGHV, along with trisomy 12 and del(13q14).

DIAGNOSES: He was diagnosed with LPL with IgG-λ monoclonal immunoglobulin and free λ light chains, classified as low risk per the Revised International Prognostic Scoring System.

INTERVENTIONS: The patient received 3 cycles of bendamustine plus rituximab therapy.

OUTCOMES: The blood cell count returned to normal and the spleen and lymph nodes were significantly reduced. Serum M protein levels decreased, and no obvious increase in B lymphocytes or plasma cells was found in the bone marrow. The patient achieved partial remission.

LESSONS: This case highlights the diagnostic and therapeutic challenges associated with the IgG-λ subtype of LPL, an uncommon variant of this rare malignancy. This report provides valuable insights into the clinical presentation, pathological features, molecular alterations, and treatment outcomes of this rare disease.