Primary mediastinal anaplastic alk-1-positive large-cell lymphoma of T/NK-cell type expressing CD20

We describe an unusual case of ALK-1-positive primary mediastinal lymphoma with the morphology of an anaplastic large-cell lymphoma (ALCL) of T/NK cell type but expressing CD20. This tumour had T/NK morphology and immunophenotype, as demonstrated by its expression of CD30, EMA, ALK-1, CD7 and TiA-1 and the lack of expression of B-cell markers other than CD20. The significance of such a co-expression of a B cell-associated antigen in a case of ALCL of T/NK cell type is discussed.