Immunohistochemical differentiation of follicular lymphoma from florid reactive follicular hyperplasia with monoclonal antibodies reactive on paraffin sections.

In this study monoclonal antibodies which recognize lymphoid-associated antigens on paraffin sections (LN1, MB2, L26, MT2, UCHL1) have been evaluated to assess their usefulness in the distinction between reactive and neoplastic lesions of lymphoid follicles. Thirty-three follicular lymphoma samples and 36 reactive samples (lymph nodes and tonsils) were analyzed. MT2 appeared as the most valuable immunophenotypic marker as emerged from a comprehensive quantitative evaluation of 2329 reactive follicles and 2288 neoplastic follicles performed on MT2 immunostained sections. MT2-positive follicles were found in all lymphoma samples but one. Overall 1908 of 2288 neoplastic follicles were judged as positive whereas no follicles with comparable strong MT2 immunoreactivity could be found in non neoplastic samples. These latter showed weak MT2 positivity only in about 10% (224/2329) of reactive follicles. This study confirms that MT2 follicular positivity can be considered a reliable marker of follicular neoplasia, although negative results ought to be considered with caution. The detection of centrofollicular cells outside the germinal centers, which is considered a reliable criterion of follicular neoplasia, was highly improved by LN1 immunostaining. On the other hand pan-B antibodies such as L26 and MB2 were less informative because of the large number of B-lymphocytes observed in interfollicular areas of nonneoplastic samples.