CLL is differentiated from Mantle Cell Lymphoma by

Mantle cell lymphoma (MCL) and chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL) share many morphologic and immunophenotypic features. In addition to histomorphologic examination, it is customary to use the absence of CD23 to differentiate MCL from CLL/SLL. ref - Harrisons internal medicine 20thediton pg764-767