An intermediately (between a low grade and high grade lymphoma) aggressive CD5 positive CD23 negative B-cell lymphoma that is usually due to t(11;14) leading to the overexpression of Cyclin D1 (BCL1). This is in contrast to CLL which is usually CD5+,CD23+ and BCL1 (CyclinD1) negative.
Atlas Link: Mantle Cell Lymphoma