An uncommon case of de novo CD10+ CD5- mantle cell lymphoma mimics follicle center B cell lymphoma.

Mantle cell lymphoma (MCL) is a mature B-cell lymphoma characterized by expression of CD5, overexpression of Cyclin D1 as a result of chromosomal translocation t(11;14)(q13;q32), and poor prognosis. Cases of MCL lacking CD5 expression as well as cases with coexpression of CD5 and CD10 have also been reported. Here we describe an uncommon case of de novo MCL with expression of CD10, but not CD5, mimicking lymphoma of germinal center-derived B cells. The lymphoma cells in this case demonstrated a diffuse pattern of proliferation, and were strongly positive for Cyclin D1 by immunohistochemical stain. Fluorescence in situ hybridization studies demonstrated the presence of t(11;14)(q13;q32) involving BCL1, but not chromosomal translocations involving C-MYC or BCL2, confirming the diagnosis of MCL. This case further highlights the importance of comprehensive immunophenotypic and genetic characterization in the diagnosis and classification of B-cell lymphomas.