IMMUNOHISTOCHEMICAL DISTINCTION OF FOLLICULAR LYMPHOMA FROM FOLLICULAR HYPERPLASIA IN FORMALIN-FIXED TISSUES USING MONOCLONAL-ANTIBODIES MT2 AND BCL-2

It is well recognized that distinguishing between follicular lymphoma and follicular hyperplasia may be difficult in some cases when fresh t issue is not available for surface immunoglobulin or gene rearrangemen t studies. A recent study performed primarily on BS-fixed tissues has demonstrated the usefulness of monoclonal antibodies, MT2 and bcl-2, i n distinguishing follicular lymphoma from follicular hyperplasia. To f urther evaluate the usefulness of these antibodies in this setting, us ing formalin-fixed tissues, 70 cases of follicular lymphoma and 20 cas es of follicular hyperplasia were studied. No significant follicular c enter cell immunoreactivity was observed with either MT2 or bcl-2 in a ny of the 20 cases of follicular hyperplasia. In cases of follicular l ymphoma, 66 of 70 cases (94%) showed positivity for MT2 or bcl-2 or bo th antibodies; only four cases (6%) showed negative or equivocal resul ts with both MT2 and bcl-2. These results indicate that MT2 and bcl-2, when used in combination, may be useful in distinguishing follicular lymphoma from follicular hyperplasia in formalin-fixed tissues in the majority of cases. Further subdividing cases of follicular lymphoma in to the three subtypes showed a pattern of decreasing immunoreactivity with bcl-2 in the following order: follicular small cleaved, follicula r mixed, and follicular large cell types. This pattern was not observe d with MT2.