A Rare Case of Cutaneous Extramedullary Hematopoiesis in Chronic Myeloid Leukemia.

Cutaneous extramedullary hematopoiesis (CEH) is a rare manifestation of extramedullary hematopoiesis (EMH), a process typically associated with fetal development or myeloproliferative neoplasms. EMH most commonly involves the spleen, liver, and lymph nodes, with CEH being exceedingly rare in chronic myeloid leukemia (CML). Here, we present a 34-year-old Hispanic male with multiple bilateral lower extremity lesions, right buttock and leg pain, fatigue, and splenomegaly, who was found to have chronic-phase CML. Punch biopsy of one of the skin lesions demonstrated dermal infiltration by maturing hematopoietic elements, including granulocytes, megakaryocytes, and erythroid precursors, with fluorescence in situ hybridization (FISH) testing confirming a neoplastic extramedullary hematopoietic infiltrate with the presence of BCR::ABL1 fusion. Initial treatment included hydroxyurea and dasatinib; however, after chronic-phase CML was confirmed, therapy was transitioned to imatinib, resulting in resolution of B symptoms, normalization of WBC counts, and reduced leg swelling. This case underscores the importance of distinguishing CEH from aggressive disease states, such as blast-phase CML or myeloid sarcoma, through comprehensive histopathological and immunohistochemical analysis.