Clinical course and treatment response. (A) Blood LDH levels in synopsis with treatments over time. (B) Initial bone marrow aspirate (left; Wright-Giemsa stain, magnification ×100) and histology (right; hematoxylin and eosin [H&E] stain, magnification ×20). (C) Positron emission tomography scan of the neck with enhanced signal in lymph nodes and lymphoid tissues (left, arrows) and lymph node histology showing leukemia infiltration (right; H&E, magnification ×4). (D) Leukemia cutis in skin biopsy. Magnification ×4. (E) Core biopsy demonstrating bone marrow leukemia in progressive relapse (H&E, magnification ×10). (F) Response to larotrectinib represented by blood blast counts over time (left) and bone marrow biopsy histology (middle and right; H&E, magnification ×4). (G) Autopsy results. (a) Gomori methenamine-silver stain demonstrating invasive aspergillosis. Magnification ×20. (b-c) Bone marrow histology (H&E) showing paucicellular areas, abundant necrosis, rare patches of viable leukemia (short arrows), and histiocytes and myeloid elements (long arrows). Magnification ×4 (b) and ×100 (c). (d) Necrotic lymph node (H&E, magnification ×4). (e) Normal skin (H&E, magnification ×10). (A-G) Days refer to time from diagnosis, except in panel F, which shows days from larotrectinib treatment start. Blin, blinatumomab; Crizo; crizotinib; CSC, consolidation chemotherapy; HAM, high-dose cytarabine and mitoxantrone; IC, induction chemotherapy; Ino, inotuzumab; LDC, lymphodepletion chemotherapy.