Clinical and Biological Features Of Monoclonal B-Cell Lymphocytosis In Patients Referred To Hospital

Monoclonal B-Cell Lymphocytosis (MBL) is a frequent condition characterized by a clonal B-cell population detected in the blood or bone marrow, in otherwise asymptomatic individuals.A small proportion of patients with MBL need clinical attention. Its prevalence is around 3-5% in healthy adults over age 40 and rises with age. The largest studies of MBL features are focused on healthy population, therefore additional data regarding the population referred to hospital are necessary. Genotype and immunophenotype data are well described in the literature so far, but a comprehensive framework of the condition is still required. Data of features not well described heretofore like bone marrow pattern of infiltration would help in the differential diagnosis.

The aim of this work was to analyze the clinical and laboratory findings of MBL reclassified from CLL or other B-cell lymphoproliferative disorders (LPD) with peripheral involvement, referred to a centre.

Three hundred seventy-one LPD patients with peripheral blood involvement diagnosed between years 2000 and 2009 in a single centre were revised to reclassify them according to the World Health Organization consensus cut-off of 5x10⁹/L circulating B cells. From those reclassified as MBL, blood count, biochemistry, immunophenotype, cytogenetics, bone marrow trepine biopsy and results of CT screening were registered, as well as treatment and outcome data. Only those patients who were followed in our centre were included.

Seventy-three LPD (20%) were reclassified as MBL, with a median age of 72 years (range: 42-94) and a 52% of males. Proportions of CLL-like LPD, CD5 negative non CLL-like and CD5 positive non CLL-like switched from 65%, 21% and 14% to 84%, 7% and 9% after the reclassification. In only seven out of 41 patients the bone marrow was not infiltrated, while the majority had an interstitial and a mixed nodular and interstitial infiltration (44% and 36%, respectively). Only 2 out of 49 patients had a concomitant infection with hepatitis C virus. Fifty-nine % of patients had a FISH alteration, predominantly chromosome 13 deletion. Thirty-seven out of 69 patients (54%) fulfilled criteria of LPD progression, with 10 patients (15%) requiring treatment (7 out of them because of progression of CLL). The mean (SD) B-lymphocyte count at diagnosis of patients with LPD progression was 3.58x10^9/L (0.9x10^9/L) versus 3.03x10^9/L (1.1x10^9/L) in those who did not progress, p=0.023. The 12-year progression free survival of the whole series was 38% (CI 95% 23-53) with a median of 4.08 years (range: 2.3-5.8). The 12-year overall survival was 54% (29-79), with a median follow-up of 7.73 years (1.7 – 12.9).

An important proportion of LPD with peripheral involvement can be reclassified to MBL, with a higher prevalence of CLL-like LPD than the global set of patients. The pattern of bone marrow infiltration was predominantly interstitial, followed by a mixed pattern of infiltration. A high percentage of patients in this series evolved to LPD, but a small subset required specific treatment. The patients with LPD progression had a significantly higher B-lymphocyte count than those who did not.

No relevant conflicts of interest to declare.