Histopathology of the spleen, liver, and bone marrow in hepatosplenic γδ T-cell lymphoma. In the spleen, (A) the general architecture is preserved with marked hyperplasia of the red pulp; (B) at high magnification, medium-sized neoplastic cells are located within the cords and sinuses of the red pulp (patient 15), and (C) histiocytes are admixed (patient 12), disclosing some features of hemophagocytosis. In the liver (D), neoplastic lymphoid cells infiltrate variably dilated sinusoids (patient 1). In bone marrow biopsy (E-I), the marrow is usually hypercellular (E) and exhibits an elective sinusal infiltrate composed of medium-sized atypical lymphocytes (E-F), which is more obvious in panel E (patient 7) than in panel G (patient 17). In the latter, the mild infiltrate is strongly highlighted by immunostaining showing the CD3⁺CD5^- phenotype of the neoplastic cells (H-I). In rare instances, atypical cytology was observed at initial examination (J), with presence of pleomorphic medium and large cells within the hepatic sinusoids (patient 14). Neoplastic cells display a nonactivated cytotoxic profile with strong granular cytoplasmic staining for TIA1 (K) but absence of granzyme B expression (L), as shown in the spleen (patient 2) (the arrow indicates the rare Granzyme-B-positive lymphocytes that act as internal positive control). Cytologic features of progression with blastic appearance were observed in the heavy infiltrated bone marrow of patient 1, at relapse (M); compare the cytology with that observed in the liver at initial examination, as seen in panel D.