Relative distribution of tumour cells and reactive cells in follicular lymphoma.

Follicular lymphoma is the most common low-grade B-cell lymphoma. It is characterized by at least a partial follicular growth pattern in the majority of cases, by the morphological resemblance of the tumour cells to follicle centre centroblasts and centrocytes, and by the distinctive expression of Bcl-2 protein as a consequence of a translocation between chromosomes 14 and 18, resulting in the juxtaposition of Bcl-2 and the immunoglobulin heavy chain locus. It is not known whether the follicular growth pattern of follicular lymphoma is a consequence of properties of the tumour cells, or whether the tumour cells invade and gradually occupy a niche generated by a normal T-cell-dependent B-cell response. This study has identified cases of follicular lymphoma in which the tumour cells are apparent within a normal reactive germinal centre background. The reactive background has been investigated in these cases and also in cases showing a more characteristic appearance, in which entire malignant follicles appear to be Bcl-2-positive, as assessed by microdissection and analysis of clonality by the polymerase chain reaction (PCR). A reactive oligoclonal background was observed in all cases studied, characteristic of a normal follicle centre response. These data suggest that the progression of follicular lymphoma is dependent on the normal germinal centre microenvironment. Disruption of this dependence might be considered as a novel therapeutic strategy.