Most cases of MCL have the following phenotype: CD5 + , CD19 + , CD20 + , surface IgM + /IgD + , Cyclin D1 + , SOX11 + , BCL2 + , BCL6 − , CD10 − , CD23 − , CD200 − , but aberrant phenotypes are seen in 10–15% of cases which might cause diagnostic difficulties. The gene discussed is CD5; the disease is mantle cell lymphoma.