The monoclonal B-cell lymphocytosis (MBL) introduced as new entities in the 2008 WHO classification, are defined by circulating B-cell clone < 5.109/L without organomegaly and previous and/or simultaneous lymphoproliferative disorders. The MBL were subclassified in MBL CLL type (the most frequent), MBL atypical CLL type and MBL non-CLL type (rarely reported in literature). Here the clinic, cytologic, immunologic and genetic features of MBL non-CLL type were described from a series of 34 cases. As previously reported, present cases presented immunologic and genetic similarities to MZL and could be associated to the new proposed entity CBL-MZ (clonal B-cell lymphocytosis of marginal zone origin). In addition, few cases presented similarities to splenic diffuse red pulp lymphoma (SDRPL). In conclusion, according to the literature, MBL with non-CLL type (assimilated to CBL-MZ) may be a premalignant state of MZL and/or SDRPL.
Keywords: CBL-MZ; NGS; SDRPL; flow cytometry; marginal zone lymphoma; monoclonal B-cell lymphocytosis.