Bcl-2 protein in centrocytic lymphoma; a paraffin section study

Bcl-2 is an inner mitochondrial membrane protein which blocks apoptosis. Although present in many B cells, the vast majority of follicular center cells do not have detectable bcl-2 protein. The bcl-2 gene is translocated in most conventional small cleaved follicular center cell (SCFCC) lymphomas (centroblastic/centrocytic) but not in centrocytic lymphomas (CC). The translocated gene in the SCFCC lymphomas leads to 'aberrant' bcl-2 expression by the neoplastic follicular center cells. The frequency with which the normal non-translocated gene is expressed in CC lymphomas is, however, not well documented. Paraffin sections from 22 cases of centrocytic lymphoma were therefore stained with an anti-bcl-2 antibody. Genotypic studies in 14 cases demonstrated bcl-1/PRAD1 (cyclin D1; CCND1) rearrangements in ten and bcl-2 rearrangements in none. All centrocytic lymphomas demonstrated bcl-2 protein expression in the majority of neoplastic cells. Negative staining residual follicular centers were identified in four cases emphasizing the mantle zone growth pattern of a subset of CC lymphomas. Expression of bcl-2 protein in the absence of bcl-2 gene rearrangement is a feature shared by centrocytic lymphomas and mantle zone cells. However, because this type of bcl-2 expression is not specific for B-cells of the mantle zone, it does not further elucidate the true cell of origin for the centrocytic lymphomas.