Overlapping morphologic and immunophenotypic profiles in small B-cell lymphoma. A report of two cases.

We present two cases of small B-cell lymphomas of particular diagnostic interest because the histological patterns were at variance with their immunophenotype. One of these lymphomas, involving the gallbladder and duodenum, showed a marginal zone lymphoma-like (MALT type) pattern of cellular infiltration with CD5 negativity but (unexpectedly) Cyclin D1 positivity. Fluorescence in situ hybridization analysis of this case was performed because of the aberrant expression of Cyclin D1, and was clearly positive for the Cyclin D1 gene translocation. The second case, occurring in a lymph node, showed the typical growth pattern of a follicular lymphoma but it had an atypical immunophenotype, namely, expression of Cyclin D1, CD10, and Bcl2 and focally Bcl6, accompanied by a lack of CD5 and CD23. The Cyclin D1 gene translocation was detected by fluorescence in situ hybridisation (FISH), whereas c-myc and Bcl2 genes translocation were absent. Numerical chromosomal changes, which were visualized for chromosomes 8, 11, and 18 could be correlated to the aberrant immunoprofile. In this context, we discuss the diagnostic value of Cyclin D1, CD5, CD23, CD10, Bcl6 markers revealed by immunohistochemistry, as well as the significance of detection by FISH of chromosomal translocations such as t(11;14) and t(14;18). The question still remains as to whether such cases should be designated as specific lymphoma entities or reported as unclassifiable and the chromosome aberration reported