Follicular lymphoma associated with marked proliferation of Mott cells

Excerpt

We present a case of follicular lymphoma (FL) in which plasmacytic differentiation of cells in bone marrow and lymph nodes was observed. The abnormal cells contained Russell bodies, i.e., eosinophilic intracytoplasmic immunoglobulin globules. Such cells are usually called Mott cells, and their presence indicates plasmacytic differentiation. The patient was a 69-year-old man who complained of a sense of abdominal fullness and edema of both legs for 1 year. Computed tomography revealed a bulky mass in his abdomen and marked splenomegaly. Laboratory findings were as follows: white blood cells, 4140/μL; hemoglobin, 11.8 g/dL; platelets, 87 × 10³/μL; lactate dehydrogenase, 319 U/L; and soluble interleukin-2 receptor, 704 U/mL. The level of IgM in serum was increased to 646 mg/dL and was consistent with detection of IgM monoclonal gammopathy by electrophoresis. Hematoxylin–eosin (HE) staining of a lymph node biopsy revealed an indistinct follicular pattern (Fig. 1a). Neoplastic follicles consisted of cleaved small lymphocytes (centrocytes) with scattered large cells (centroblasts) (Fig. 1b). Of note, infiltration of hypersecretory cells with eosinophilic intracytoplasmic immunoglobulin globules (Russell bodies), the so-called Mott cells, was observed (Fig. 1c, d). The Mott cells were distributed mainly in the interfollicular area and observed less frequently in the intrafollicular area (Fig. 1b). Immunohistochemically, the centrocytes and centroblasts showed positivity for CD20, CD10 (partially), and BCL-2, and negativity for CD3, BCL-6, MUM1, and CD138. The Mott cells showed positivity for MUM1, CD79a, CD10 (partially), and BCL-2, and negativity for CD20 and CD138 (data not shown). In addition, the Mott cells showed λ light chain restriction (Fig. 1e, f). Bone marrow puncture showed infiltration of lymphoma cells and associated Mott cells, highlighting bone marrow involvement of the tumor. Although the Mott cells were negative for CD138, their immunophenotype of CD20⁻, CD79a⁺, and MUM1⁺ reflects their plasmacytic differentiation. Chromosomal analysis of the lymph node biopsy showed 47, XY, +12 (6 of 10 analyzed cells)/47, XY, ?t(5;14)(q35;q24), +12 (1/10 cells)/48, XY, −5, del(6)(q?), −7, −8, −12, +6mar (1/10 cells), and other abnormal cells with unclear karyotypes (2/10 cells). Upper gastro-intestinal endoscopic examination detected no lymphoma cell infiltration. Based on the above findings, a diagnosis of stage IV FL grade 1 associated with the differentiation of the cells to Mott cells was made. The patient showed partial response to treatment with R-CHOP (cyclophosphamide, vincristine, doxorubicin, prednisolone, rituximab). At present, he continues to maintain a partial response to maintenance therapy with rituximab. Although some reports have suggested that the clinical course of FL with plasma cell differentiation is aggressive, the clinical course of FL with Mott cells remains unclear due to the small number of similar reports [1].

…