(Table 14) Key changes in the current edition of the classification include: (1) inclusion of clonal plasmacytoid dendritic cell (pDC) diseases in this category; (2) moving follicular dendritic cell sarcoma and fibroblastic reticular cell tumor to a separate category; and, (3) addition of Rosai-Dorfman disease (RDD) and ALK-positive histiocytosis as disease types. The gene discussed is ALK; the disease is sinus histiocytosis with massive lymphadenopathy.