A Rare Case of Non-IgM Lymphoplasmacytic Lymphoma with Unusual Lack of Immunoglobulin Light Chain Production.

BACKGROUND Non-IgM lymphoplasmacytic lymphoma (LPL) is a rare subtype of LPL, constituting less than 5% of the cases, and is often associated with IgG, IgA, or light chain paraproteins and is rarely a non-secretor. Non-IgM LPL remains poorly studied, and the differential diagnosis from other small B-cell lymphomas with plasmacytic differentiation and plasma cell neoplasm is challenging. CASE REPORT A 67-year-old woman presented with weight loss, persistent anemia, and borderline leukopenia. Serum protein electrophoresis and immunofixation demonstrated a faint IgG and kappa band against a dense polyclonal background. Bone marrow biopsy revealed hypercellular marrow with involvement by abnormal B cells with undetectable surface and cytoplasmic immunoglobulin light chains. Interestingly, these B cells showed no expression of light chains or production of IgG and IgM; however, they showed production of intracytoplasmic IgA. The concomitant neoplastic plasma cells also displayed no definitive light chain expression. Both IgH and IgK gene rearrangements were positive for clonal process. Molecular studies showed positive MYD88 L265P mutation and CXCR4 mutation (c.1013C>G). The overall findings confirmed marrow involvement by non-IgM LPL. The patient received 6 cycles of rituximab and bendamustine treatment, and no residual marrow involvement was found on the follow-up bone marrow biopsy. CONCLUSIONS We report a non-IgM LPL case featuring no light chain production and no heavy chain secretion, which we believe is the first reported case of this kind in the literature.

ALK-positive Large B-Cell Lymphoma With Multiple Epithelial Antigen Expression and PABPC1::ALK Fusion : A Novel Molecular Alteration.

Anaplastic lymphoma kinase (ALK)-positive large B-cell lymphoma (LBCL) is a very rare type of LBCL with an aggressive clinical course and poor prognosis. This diagnosis can be challenging given the varied morphology (immunoblastic, plasmablastic, or anaplastic), frequent lack of B-cell antigens, and especially in cases with expression of epithelial antigens. Here, we report a case of ALK-positive LBCL with unusual expression of 4 epithelial-associated markers (AE1/AE3, CK8/18, EMA, and GATA3) and novel poly(A) binding protein cytoplasmic 1 (PABPC1) :: ALK fusion which has not been previously reported in this entity. This case also emphasizes the use of comprehensive immunophenotyping that includes multiple lineage-specific antibodies when faced with a malignancy without a clear differentiation to avoid misdiagnosis. This case only achieved partial response to combination chemotherapy, radiation, and ALK inhibitor regimens, and furthers our understanding of this uncommon lymphoma.