A 23-year-old man with a history of Ph-Like B-cell acute lymphoblastic leukemia (B-ALL) with JAK2 rearrangement presented with innumerable skin lesions developing over 1 week. Before presentation, he had multiple relapses of his B-ALL and underwent autologous UCD-19 chimeric antigen receptor (CAR) T-cell therapy. Lesions appeared 1.5 months after completion of therapy. Biopsies showed new onset myeloid sarcoma (MS), with continued remission of B-ALL. 18F-FDG PET/CT showed numerous markedly hypermetabolic soft tissue lesions located in the skin and subcutaneous tissues, muscles, osseous structures, mucosa, pleura, mediastinum, peritoneum, retroperitoneum, and testes.