Mantle cell lymphoma (MCL) is a mature B-cell neoplasm that expresses B-cell markers CD19, CD20 (shown here in the left panel), CD22, and CD79a. Similar to chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL), the expression of CD5 (shown in the right panel) is seen in mantle cell lymphomas (MCL). The differentiating feature between the two entities is CD23 positivity in CLL/SLL whereas MCL is usually CD23 negative. It must be remembered that bona fide cases of MCL that are CD5 negative or CD23 positive (see next image) have been reported. Image courtesy of: Genevieve Crane, MD, PhD, Johns Hopkins Hospital, Baltimore, Maryland, USA.