Mantle cell lymphoma, light micrograph. A subset of mantle cell lymphomas (MCL) with particularly aggressive course are characterized by the presence of blastoid cells or pleomorphic cells. Notwithstanding their morphology, both cell types have the same phenotypic and genotypic features (cyclin D1 overexpression; t(11;14)(q13;q32) as the classic MCL. The blastoid cells (shown here in a case of MCL involving a lymph node) have medium size, round or slightly irregular nuclei with finely dispersed chromatin, inconspicuous nucleoli, and a high mitotic index. Tingible-body macrophages creating a "starry-sky" pattern may be present. The differential diagnosis in such cases includes lymphoblastic lymphoma and nodal involvement by acute myeloid leukaemia.