OBJECTIVETo investigate the clinicopathologic and molecular characteristics of acute promyelocytic leukemia(APL) developed during imatinib therapy for gastrointestinal stromal tumors(GIST).

METHODSA 49-year-old woman was hospitalized for abdominal pain. The abdominal CT revealed a gastric mass. Laparoscopic resection of the tumor was performed. The histopathologic analysis showed poorly differentiated malignant cell infiltration with epithelioid features. Immunohistochemistry staining of these cells was positive for CD117 and CD34. GIST was confirmed and imatinib treatment was given.

RESULTSAfter 1 year,the patient developed progressive pancytopenia. Bone marrow aspirate showed marked hyperplasia of bone marrow cells with 92.5% promyelocyte, consistent with APL. Cytogenetic analysis demonstrated t(15;17)(q22;q21) as the sole abnormality. PML/RARα fusion gene was positive and Kit mutation was negative. After combined treatment with ATRA, arsenic trioxide and idarubicin, patient achieved cytogenetic and molecular remission.

CONCLUSIONThe metachronous coexistence of GIST with APL is uncommon. The potential nonrandom association and causal relationship between these malignancies remained to be investigated. Further studies would be necessary to clarify the relationship between imatinib and secondary malignancies in GIST patients.