Lack of Bcl-2 expression in feline follicular lymphomas

Bcl-2, an anti-apoptotic protein, is commonly overexpressed in follicular lymphomas in humans. This is usually the result of a chromosomal translocation that transposes the Bcl-2 gene into the immunoglobulin gene locus. The immunohistochemical assessment of this overexpression can be used as a tool for the differentiation of follicular lymphoma and follicular hyperplasia. In cats, little information about the expression of Bcl-2 in follicular lymphoma exists. We investigated 18 follicular lymphomas histologically and immunohistochemically for the expression of Bcl-2, CD3, CD45R, and feline leukemia virus. Clonality was assessed by PCR for antigen receptor gene rearrangements. Although the histology resembled that of their human counterparts, diffuse expression of Bcl-2 within the follicles of the feline lymphomas, as seen in human cases, was not present. Only single cells within the follicles, comparable to the reactive controls, were positive for Bcl-2 expression. The mean survival time of 4.6 y confirmed the indolent character of the tumor. None of the clinical parameters assessed were statistically significant predictors of survival. Furthermore, a statistically significant difference in survival of animals with or without anti-neoplastic therapy was also not demonstrable.