In January 2013, a 65-year-old male presented to Korea University Anam Hospital (Seoul, Republic of Korea), with an intra-abdominal mass that was localized to the right side. The mass had presented one month previously. In addition, the patient had experienced weight loss (5 kg) during the previous four months. The medical history was unremarkable, with the exception of pulmonary tuberculosis 30 years previously, from which the patient had recovered. On physical examination, a round mass was palpated and there was tenderness of the right upper quadrant area. Hematological examination revealed a marginal decrease of hematocrit (35.8%; normal range, 37-51%) and hemoglobin (11.8 g/dl; normal range, 12.6-17.4 g/dl). Liver function tests revealed elevated alkaline phosphatase (423 IU/l; normal range, 30-120 IU/l) and gamma-glutamyl transferase (587 IU/l; normal range, 9-64 IU/l) levels. Aspartate aminotransferase, alanine aminotransferase and bilirubin levels were within the normal ranges of 3-45 IU/l, 3-45 IU/l and 0.0-0.4 mg/dl, respectively. An upper gastrointestinal endoscopy revealed a subepithelial mass with a fistulous hole on the second portion of the duodenum (Fig. 1). A total colonoscopy revealed no abnormalities. A computed tomography (CT) scan, which was acquired from the referring local clinic (Choi Kang Sik Internal Medicine, Seoul, Republic of Korea), demonstrated a large, heterogeneously enhanced lobulated mass (11.5x9.3 cm; longest diameter x greatest perpendicular diameter) with internal necrosis at the pancreaticoduodenal groove (Fig. 2A). The internal cavity of the mass was connected to the second portion of the duodenum, which was consistent with the endoscopic findings. Furthermore, an ill-defined low-attenuation lesion was identified at segment eight of the liver, abutting the bile duct and hepatic artery (Fig. 2B). Significantly enlarged lymph nodes were not observed in the abdominal cavity. In addition, a fludeoxyglucose positron emission tomography (FDG-PET) scan also revealed hypermetabolic masses in the duodenal groove and in segment eight of the liver, which was consistent with the CT scan. Abdominal MRI (magnetic resonance imaging) was also conducted for further characterization of the duodenal and hepatic masses observed on the CT scan, which confirmed the same findings. An ultrasound-guided needle biopsy of the duodenal mass was performed and pathological examination identified whirling sheets of spindle-shaped cells (Fig. 3A). Immunohistochemical staining was positive for c-Kit, but negative for cluster of differentiation 34, S-100 and desmin (Fig. 3B). Mitotic features could not be evaluated, as a surgically excised sample was not obtained. The diagnosis of high-risk GIST with hepatic metastasis was determined and the patient was treated with 400 mg imatinib, daily. The treatment was tolerated well, and the abdominal mass and distension improved significantly. After seven weeks of treatment, the follow-up abdominal CT scan revealed that the duodenal mass had significantly reduced in size (7.9x6.5 cm; longest diameter x greatest perpendicular diameter) and exhibited an increased area of internal necrosis. However, the hepatic mass had increased from 1.7x1.5 cm to 3.9x3.2 cm in diameter (longest diameter x greatest perpendicular diameter) and the right hepatic duct was markedly dilated by the mass (Fig. 4). Various enlarged lymph nodes were observed in the left gastric area, including the porta hepatis and portocaval space. The ultrasound-guided needle biopsy was repeated for the hepatic mass and histopathological examination of the biopsy specimen showed malignant cells with a glandular structure, which was consistent with adenocarcinoma. Immunohistochemical analysis exhibited c-Kit-negative and cytokeratin 19-positive staining (Fig. 5). The final diagnosis was synchronous ICC and GIST. Two weeks after the ultrasound-guided liver biopsy, the patient developed jaundice and a fever, and the total level of bilirubin increased rapidly to 9.4 mg/dl (normal range, 0.0-0.4 mg/dl). Percutaneous transhepatic biliary drainage was conducted along with antibiotic treatment and administration of imatinib was withheld to allow the patient to recover from the condition. An abdominal CT scan following three weeks of conservative treatment revealed an increase in size of the liver mass (5.3x3.9 cm; longest diameter x greatest perpendicular diameter) with portal vein thrombosis, and the size of the duodenal mass had also increased to 9.5x8.7 cm (longest diameter x greatest perpendicular diameter). The treatment regimen became focused towards the ICC, which was associated with a poorer prognosis. Due to the well-known toxicity of combined chemotherapy, administration of imatinib was terminated and the patient was treated with intravenous gemcitabine (100 mg/m2 for 30 min, days 1 and 8) and cisplatin (25 mg/m2 for 1 h, days 1 and 8) every three weeks for four cycles. During chemotherapy, the abdominal mass reappeared, as a follow-up CT scan, performed six weeks following treatment, revealed a prominent increase in the size of the duodenal mass (10.7x10 cm; longest diameter x greatest perpendicular diameter). However, the hepatic mass did not demonstrate a significant change in size during that interval. As the patient had tolerated the initial chemotherapy well, combined chemotherapy (consisting of imatinib, gemcitabine and cisplatin) was initiated for symptom control and treatment of the GIST. The addition of imatinib resulted in the duodenal mass decreasing significantly and the patient exhibited a good response to the treatment. However, certain toxicities are associated with combined chemotherapy, such as grade 1 bone marrow suppression, as observed in the present case. The follow-up CT scan revealed disease progression of the ICC, whereas the size of the GIST mass had decreased. The treatment modality was altered, due to refractory cholangiocarcinoma, from chemotherapy to radiation therapy (daily dose of 180 Gy), whilst maintaining the imatinib treatment. To date, the patient has been undergoing treatment for one year and is tolerating the treatment well.