Mantle cell lymphoma, light micrograph. Mantle cell lymphoma is an aggressive B-cell lymphoma composed of small to medium-sized monomorphic lymphoid cells with irregular, indented, or clefted nuclei resembling centrocytes. It has also been known as mantle zone lymphoma, centrocytic lymphoma, diffuse small cleaved cell lymphoma, and intermediate lymphocytic lymphoma. It makes up about 2.5% of non-Hodgkin lymphomas in the US. The image shows mantle cell lymphoma involving the spleen.