Instances of mantle cell lymphoma morphologically mimicking other subtypes of B-cell lymphoid proliferation.

Mantle cell lymphoma is a well-characterized category of mature B-cell lymphoma with aberrant coexpression of CD5 antigen. This subtype of lymphoma is genetically defined by t(11;14) resulting in upregulation of cyclin D1 protein. In clinical practice, mantle cell lymphoma is typically diagnosed based on combination of morphology, CD20/CD5 coexpression, and nuclear staining of cyclin D1 protein by immunohistochemistry. Although other neoplastic processes can also be cyclin D1 positive, documentation of cyclin D1 positivity in a CD5-positive B-cell process is virtually diagnostic of mantle cell lymphoma. However, on morphologic grounds, it is well known that mantle cell lymphoma can mimic other subtypes of B-cell lymphoid neoplasm. We identified several unusual examples of immunohistochemically confirmed cyclin D1-positive mantle cell lymphoma with morphologic features overlapping with a wide variety of other subtypes of mature B-cell lymphomas including follicular, marginal zone, small lymphocytic and Burkitt lymphoma.