[Monoclonal plasmacytic differentiation in small-cell lymphomas of B-cell origin: immunocytoma versus other types]

We have studied the morphological and immunohistochemical features of monoclonal cytoplasmic Ig (c-Ig) production in the biopsy material of 161 small B-cell non-Hodgkin's lymphomas to verify a frequency of the plasmacytic/plasmacytoid differentiation of tumor cells for the aims of their differential diagnosis. The analyzed differentiation was identified in all the cases of immunocytoma (n = 20/20), in 2/3 of MALT-lymphomas (n = 24/38) and 1/2 of monocytoid B-cell lymphoma cases (n = 4/7), in 1/5 of centroblastic-centrocytic lymphoma cases (n = 12/60) and rarely in centrocytoma (n = 4/36). We conclude that a plasmacytic differentiation is not an unique feature of the immunocytoma. For the differential diagnosis, a histological analysis and not a proof of monoclonal c-Ig itself seems to be decisive. The obtained results are discussed in relation to the histogenesis of small B-cell lymphomas, which represent a neoplastic counterpart of the reactive B-cells at different stages of their maturation and differentiation.