Follicular lymphoma with plasmacytic differentiation accompanied by monoclonal IgG gammopathy.

: A 59-year-old woman presented with high serum total protein, detected on a screening examination. Laboratory tests revealed high plasma levels of M-protein (IgG-λ), and FDG-PET/CT revealed systemic lymph node swelling and a large tumorous mass in the abdominal cavity. Bone marrow aspirates contained 8.4% plasma cells and approximately 30% abnormal small lymphocytes. A biopsy of the left supraclavicular lymph node was initially interpreted as lymphoplasmacytic lymphoma (LPL). However, chromosomal analysis of the lymph node demonstrated an unusual karyotype with t (14;18) (q32;q21). FISH analysis for the IgH-BCL2 fusion gene was positive. Furthermore, the MYD88 L265P mutation was not detected in tumor cells. Based on these findings, this case was determined to be a type of follicular lymphoma with plasmacytic differentiation. We considered that this case was an important example emphasizing the importance of karyotypic examination for lymphoma classification.