Although the differential staining of the epithelial membrane antigen (EMA) and a weak PAX5 expression could serve to establish a differential diagnosis, HRS cells contain Ig gene rearrangements in more than 98% of cases [47] whereas ALCL, ALK-positive show clonal rearrangements of the T cell receptor (TCR) genes in approximately 90% of the cases [48]. Here, ALK is linked to anaplastic large cell lymphoma.