Immunohistochemical expression of Mum-1, Oct-2 and Bcl-6 in systemic anaplastic large cell lymphomas.

Several transcription factors predominantly used for B-cell lineage identification are also expressed in a small percentage of T cells within germinal centers and interfollicular areas. The aim of the study was to evaluate the expression of Mum-1, Oct-2 and Bcl-6 in systemic anaplastic large cell lymphoma. Thirty cases of anaplastic large cell lymphoma were retrieved from our archives and tissue microarray constructed. Immunohistochemistry was carried out using an avidin-biotin peroxidase complex method. A predominance of nuclear staining was observed for all transcription factors. Mum-1 was positive in all but one case (96.7%). Half of the cases displayed Oct-2 expression (15/30 cases). A considerable number of cases also had Bcl-6 expression (9/30). Bcl-6 staining was noted to be more common in ALK positive cases. Our findings emphasize that these markers are not restricted to B-cell lineage and that extensive expression can be observed in anaplastic large cell lymphoma of T/null cell phenotype.