ABSTRACT
A localized extramedullary tumor mass composed of immature cells has been reported in association with acute myeloid leukemia, myeloproliferative disorders, myelodysplasia in blast transformation or chronic myeloid leukemia with trilineage hematopoiesis, as well as in patients with no known hematological disorder. Although this tumor may involve anywhere in the body and give rise to a variety of signs and symptoms, there are several case reports of extramedullary tumor in Korea which described the involvement of the gastrointestinal tract. We report the occurrence of gastric extramedullary tumor and lymphoid blast crisis in a patient with complete remission after lymphoblastic transformation of chronic myelogenous leukemia. Endoscopic biopsy for gastric elevated lesion showed diffuse lymphoblast infiltration with TdT (terminal deoxynucleotidal transferase) and CD20 positive immature cells.