Lymph node and BM morphology with corresponding FC histograms from patient 10 with AITL and AML. (A-B) Lymph node was effaced by an infiltrate of small to intermediate-sized lymphoid cells with moderate amounts of pale cytoplasm in a background of mixed inflammatory cells and vascular proliferation (A, hematoxylin and eosin stain, original magnification ×400). (B) The neoplastic T cells expressed PD-1 by immunohistochemistry (original magnification ×400). (C) FC analysis of the lymph node demonstrated an abnormal T-cell population that was surface CD3(−) and CD5(+) (aqua population). These cells were also positive for CD4, CD2, and PD-1 (not shown). The findings were consistent with AITL. (D-F) Subsequent BM biopsy demonstrated aggregates of atypical lymphoid cells as well as increased blasts and promonocytes. (D) Hematoxylin and eosin–stained core biopsy, original magnification ×400. (E) CD3 immunohistochemistry performed on the core biopsy specimen highlighted the neoplastic T cells (original magnification ×400). (F) Wright-Giemsa–stained aspirate smear demonstrated frequent blasts/promonocytes as well as dysgranulopoiesis (inset) and dyserythropoiesis (original magnification ×1000). (G-I) FC analysis of the BM detected a surface CD3(−), CD5(+) abnormal T-cell population similar to that seen in the lymph node (aqua population) (G) as well as a small abnormal CD34(+) myeloid blast population with dim CD7 expression (red population) (H) and an expanded CD64(+) monoblast population (pink population) (I). The findings were consistent with BM involvement by both AITL and AML with monocytic differentiation.