Gastrointestinal stromal tumors (GISTs) are mesenchymal tumors that mainly arise in the gastrointestinal tract. They are usually asymptomatic and are incidentally discovered during endoscopy or surgery. Diagnosis is confirmed by histological examination of the specimen. This is the case report of an asymptomatic GIST of the small intestine diagnosed by wireless capsule endoscopy. The tumor was initially suspected to be a leiomyoma, as GISTs in young adults are rare and are mainly discovered incidentally during colorectal cancer screening. The patient was a 35‑year‑old woman with occult gastrointestinal bleeding, with a normal medical history. An endoscopic assessment of the upper and lower GI tract (gastroscopy and colonoscopy) was performed, but did not reveal any abnormalities. Subsequently, an exophytic tumor initially suspected as leiomyoma or external pressure was detected in the small intestine by capsule endoscopy. A computed tomography scan was suggestive of a soft tissue tumor arising from the small intestine. A surgical specimen was obtained and the immunohistochemical examination revealed that the tumor was positive for CD117 and discovered on GIST-1 markers, while the markers of carcinoma, melanoma and lymphoma were negative, which was consistent with a diagnosis of a low‑risk GIST with a mitotic count of <5/50 high‑power fields. In this study, we aimed to present in detail the capsule endoscopic and radiological characteristics, as well as the findings of the histological examination of the surgical specimen. In conclusion, when occult blood is detected in the stool, even when gastroscopy and colonoscopy reveal no abnormal findings, small intestinal lesions should be suspected. Exophytic small intestinal GISTs, although rare, particularly in younger patients, they should be considered by physicians in the differential diagnosis of obscure GI bleeding of unknown origin, in order to reduce morbidity and mortality. Capsule endoscopy may be considered to be the first choice as a diagnostic tool for obscure GI bleeding.

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