[Chronic myeloid leukemia with an in-frame exon 4 deletion in ABL1 with acute abdomen due to an intrapelvic bulky mass as the initial symptom].

A 23-year-old woman was admitted to our hospital because of rapidly developing lower abdominal pain. Computed tomography revealed ascites, splenomegaly, and a huge mass that occupied the pouch of Douglas and surrounded her uterus. A markedly elevated white blood cell count of 495×109/l and the identification of the BCR-ABL1 fusion gene led to the diagnosis of chronic myeloid leukemia (CML). Although neither an increase in the blast percentage nor any additional chromosomal abnormality was observed in the patient, CML was considered in the blast phase because of extramedullary disease infiltration. Dasatinib was administered with the temporal use of hydroxyurea and VP-16, which resulted in rapid disappearance of her intrapelvic mass and complete hematologic response within 1 month. She refused to undergo allogeneic hematopoietic stem cell transplantation and continued to take dasatinib, achieving complete cytogenetic and major molecular responses within 5 and 11 months, respectively. CML cases initially presenting with extramedullary tumors are rare. Furthermore, in our case, a mutational analysis at diagnosis revealed an in-frame exon 4 deletion in ABL1, which is reported to decrease cell proliferation. This fact is intriguing because her clinical outcome was relatively favorable.