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Intra-abdominal desmoid tumors mimicking gastrointestinal stromal tumors - 8 cases: A case report. BACKGROUND: Intra-abdominal desmoid tumors (DTs) can mimic recurrence or progression of gastrointestinal stromal tumors (GISTs). Differential diagnosis is important to avoid unnecessary or inappropriate treatment. CASE SUMMARY: All 8 patients experienced surgical resection of GIST, and median time to diagnosis of DT was 1.8 years after surgical resection. All sites of DT were in the peritoneum around the surgical sites of GIST. The following clinical suspicion coupled with radiological findings contributed to the suspicion of intra-abdominal DTs: (1) Occurrence of a new single lesion in the peritoneum around the surgical sites of GIST; (2) uncontrolled lesion with imatinib while other lesions being controlled with imatinib; (3) well-defined ovoid shaped lesion with delayed or mild enhancement and absence of necrosis, hemorrhage, and cystic change on computed tomography; and (4) a lesion showing mild or no hypermetabolic activity on 18fluorodeoxyglucose-positron emission tomography, contrary to initially hyperactive lesion of GIST. All DTs were surgically removed except for one unresectable DT and only one DT recurred at another site of peritoneum, which was also surgically removed. CONCLUSION: Intra-abdominal DT should be a differential diagnosis for a new single lesion in patients with GIST.