Follicular lymphoma with trisomy 18 exhibiting loss of BCL-2 expression on transformation to a large cell lymphoma

Over-expression of BCL-2 in follicular lymphoma is commonly caused by a t(14;18) chromosomal translocation. Follicular lymphomas that do not carry the t(14;18) translocation but are positive for BCL-2 protein may have other cytogenetic abnormalities, including BCL-2 amplification, reciprocal translocations involving the IGK/IGL loci1 and trisomy 18.2,3 Transformation of follicular lymphoma to diffuse large B cell lymphoma is generally associated with a poorer prognosis.4,5 However, there have been no extensive studies in the literature of the BCL-2 gene and protein status in transformed diffuse large B cell lymphoma arising from BCL-2-positive follicular lymphoma. We describe a case of follicular lymphoma carrying trisomy 18 (without evidence of translocations involving the BCL-2 locus), associated with strong BCL-2 protein expression. However, the same biopsy sample contained an area of diffuse large B cell lymphoma in which BCL-2 protein was absent despite retaining the same genetic abnormality. As far as we know, there have been no other reports of BCL-2 protein that is expressed in follicular lymphoma but that ceases to be detectable after transformation. A female patient presented with a localised enlargement of a submental lymph node. No significant abnormalities were detected in her blood count and in the staging investigations. Excision biopsy revealed an enlarged and effaced lymph node. Three distinct areas, lying adjacent to each other (fig 1A,B), could be identified from their morphology and phenotype. One area comprised a classical follicular lymphoma, where the neoplastic follicles contained an admixture of centrocytes with smaller numbers of centroblasts, consistent with a grade 2 follicular lymphoma. The second area showed larger follicles that were less clearly demarcated, although their cellular composition resembled that seen in the first area. A third smaller area of the tumour consisted of diffuse …