Lymphoplasmacytic lymphoma and marginal zone lymphoma in the bone marrow: Paratrabecular involvement as an important distinguishing feature

Objectives: The differential diagnosis between bone marrow involvement by lymphoplasmacytic lymphoma (LPL) and marginal zone lymphoma (MZL) is challenging because histology and immunophenotype of both diseases overlap. We revisited the diagnostic pathology features of both diseases in the bone marrow. Methods: We studied a series of bone marrow trephine biopsy specimens from 59 patients with Waldenström macroglobulinemia without extramedullary involvement and bone marrow biopsy specimens from 23 patients with well-characterized MZL who also had bone marrow involvement. H&E- and immunoperoxidase-stained sections of bone marrow trephine biopsy specimens as well as flow cytometry and classic cytogenetics performed on aspirations were reviewed. The study was complemented with MYD88 L265P mutation analysis of all samples. Results: The most distinguishing features of LPL with respect to MZL were focal paratrabecular involvement (P < .001), the presence of lymphoplasmacytoid cells (P < .001) and Dutcher bodies (P < .001), increased numbers of mast cells (P < .001), and the MYD88 L265P mutation (P < .001). Conclusions: LPL can be reliably distinguished from MZL in the bone marrow by using a combination of pathology characteristics. Our findings stress the diagnostic importance of using the combination of the following parameters for a correct LPL diagnosis: paratrabecular infiltration, the presence of lymphoplasmacytoid cells and cells with Dutcher bodies, and an increased number of mast cells in addition to the presence of MYD88 mutation.