Despite the similarities between CLL and clinical MBL reviewed above, several biologic differences between clinical MBL and population-screening MBL have recently been identified. First, while MBL was originally thought to represent exclusively monoclonal B lymphocytes, it has become evident that biclonal (14/73)(9), oligoclonal (4/6)(15), and polyclonal (6/89)(8) cases of MBL can be identified. This observation indicates that a CLL-like phenotype (CD5+, CD20dim) is not necessarily related to the acquisition of monoclonality. These studies suggest the possibility that concomitant clones of CLL-like B-lymphocytes appear and persist in many otherwise healthy individuals where one clone may expand and, in a small subset of individuals, become predominant with time. Further investigation is now needed to elucidate the type of stimulation, antigen activation, or other events that induce some B lymphocytes to acquire the CLL phenotype.
