Morphologic transformation in 2 relapsing cases. Giemsa (A) and hematoxylin and eosin (B) staining is shown above and immunostaining is shown below. (Case A) The morphologic appearance at diagnosis was that of a lymphohistiocytic variant with scattered large neoplastic cells. ALK staining confirmed the scarcity of malignant cells (arrow). A few months later, this patient developed lung involvement consisting exclusively of large cells. (Case B) In this case, the morphologic appearance at diagnosis was that of a common-type ALCL with many large cells containing eccentric nuclei. Lymph node biopsy at relapse showed the features of a small-cell variant. Scattered large cells were strongly positive for ALK1, whereas small cells showed only moderate/weak staining.