Blastoid variant of HGBL, NOS. (A) Hematoxylin and eosin stain shows an infiltrate of medium blastoid cells with finely dispersed chromatin and inconspicuous nucleoli; touch preparation (inset) showed neoplastic cells with mostly rounded nuclei, inconspicuous nucleoli, and scant cytoplasm; the cells expressed CD19, CD20, PAX5, CD10, BCL6, and Ki-67 (>95%), but not MYC (<10%), cyclin D1, TdT, or BCL2. Additionally, stains from MUM1/IRF4, CD15, CD30, CD23, and PD-L1 were negative. (B) FISH showed normal pattern for MYC, BCL2, and IGH, but 3 copies of BCL6 (Vysis LSI IGH/BCL2 Dual Color Dual Fusion Probe, Vysis LSI BCL6 [ABR] Dual Color Break Apart Rearrangement Probe, and Vysis LSI MYC-Dual Color Break-Apart Probe; Abbott Molecular). (C) The patient, a 33-year-old woman, presented with a large mediastinal mass histologically and immunophenotypically inconsistent with B-lymphoblastic or primary mediastinal B-cell lymphoma; she attained a CR with 6 cycles of DA-EPOCH-R (etoposide, prednisone, vincristine, cyclophosphamide, doxorubicin, and rituximab) and remains in remission 3 years after therapy. Original magnification: ×600 (A).