Extramedullary involvement in refractory/relapsed HCL. (A) Computed tomography scan shows a large abdominal mass (asterisk), marked splenomegaly, and enlarged mediastinal lymph nodes (not shown). (B) Needle biopsy of the abdominal mass reveals infiltration of pancreatic glands by morphologically typical HCL cells with wide clear cytoplasm (hematoxylin-eosin; ×400). (C) HCL cells (red) strongly express the CD19 antigen (APAAP immunostaining, hematoxylin counterstaining; ×400). (D) HCL cells (brown) are also annexin-A1⁺ (immunoperoxidase staining; hematoxylin counterstaining; ×400). APAAP, alkaline phosphatase anti-alkaline phosphatase.