[Monocytoid lymphoma evolving into large-cell lymphoma].

Monocytoid B cell lymphoma (MBCL) is a newly recognized low-grade lymphoma. The malignant cells of MBCL seems to be the counterpart of reactive monocytoid B cells. The MBCL cells show a resemblance to the cells of hairy cell leukemia (HCL). The cell of MBCL exhibits immunoglobulin light chain restriction and markers of terminal BG cell differentiation. On the other hand, the HCL lack expression of CD 25 and are tartrate resistant, acid phosphatase-negative. The MBCL has prediction for elderly females. At the time of diagnosis, it is usually present in stage I or II. It may be difficult to differentiate the clinical and morphological expression of MBCL from that of any other indolent lymphoproliferative diseases, especially HCL and small lymphocytic lymphoma. Unlike other low grade lymphomas in MBCL, however, splenomegaly and bone marrow involvement are uncommon, while leukemic conversion is very rare. The MBCL transformation or association to high grade lymphomas is very unusual. In this case, it isn't clear if MBCL undergoes progression to higher grade lymphomas or if there is a "composite lymphoma" at the onset, in any case the prognosis is worse. In our patient, the involvement seemed to be only at the spleen and caeliac nodes, there was not bone marrow involvement. The fast evolution suggests that the MBCL underwent a transformation to a higher grade lymphoma. It is a common behavior in the low grade lymphoma.