FREQUENT EXPRESSION OF THE NPM-ALK CHIMERIC FUSION PROTEIN IN ANAPLASTIC LARGE-CELL LYMPHOMA, LYMPHO-HISTIOCYTIC TYPE

The revised European-American lymphoma classification recognizes a sub type of anaplastic large-cell lymphoma (ALCL), termed lympho-histiocyt ic because of its peculiar cytological composition. As in the case of classical ALCL, this tumor usually occurs in young patients and shows an excellent response to chemotherapy, but some authors have suggested that in reality this is a nonanaplastic T-cell lymphoma rich in histi ocytes. In this paper, we show that three of five cases of lympbo-hist iocytic ALCL stain with anti-ALK antibodies and can therefore be presu med to express the chimeric NPM/ALK protein secondary to (2;5) translo cation. These findings further support the inclusion of this as a type of AI;CL and not among the nonanaplastic peripheral T-cell lymphomas. Furthermore, they indicate that staining for ALK proteins is a powerf ul tool for the diagnosis of lympho-histiocytic ALCL, the recognition of which may be difficult on morphological grounds.