Prevalence and natural history of monoclonal and polyclonal B‐cell lymphocytosis in a residential adult population

Background: Monoclonal B‐cells can be detected in the peripheral blood of some adults without B‐cell malignancies, a condition recently termed monoclonal B‐cell lymphocytosis (MBL). The risk of individuals with MBL progressing to a B‐cell malignancy is unknown. Polyclonal B‐cell lymphocytosis (PCBL) has not been systematically studied in the general population. Methods: We obtained lymphocyte subset counts on 1,926 residential adults aged 40–76 years in a series of environmental health studies between 1991 and 1994. We then conducted two follow‐ups in 1997 and 2003 on consenting participants with B‐cell lymphocytosis, which included nine participants with MBL. To ascertain the clinical implications of MBL, we reviewed medical records and death certificates. Results: The overall prevalence of MBL was 0.57% (11/1,926): nine cases at baseline and two additional cases identified at follow‐up. Two (19%) MBL cases subsequently developed a B‐cell malignancy; MBL persisted in the remaining nine cases (81%). All PCBL cases where no clone emerged regressed to normal B‐cell counts over the follow‐up period. MBL was significantly more frequent in residents near a hazardous waste site than in the control populations (age‐adjusted OR 6.2; 95%CI 1.1–36.2). Conclusion: MBL confers an elevated risk for developing a B‐cell malignancy, although it occurs only in a minority of cases. PCBL is most often a transient state, but a monoclonal population can emerge and persist. Prospective studies are needed to distinguish stable from progressive forms of B‐cell lymphocytosis and to clarify the etiologic role of environmental exposures. Published 2007 Wiley‐Liss, Inc.