Gastrointestinal stromal tumors (GISTs) are non-epithelial mesenchymal tumors that usually occur in the gastrointestinal tract. Included in this group are leiomyosarcomas and leiomyomas. Furthermore, CD117, a transmembrane receptor, is the best defining feature of GISTs. CD117 is continually bound, which activates a tyrosine kinase and leads to tumorigenesis. In addition, this receptor is also expressed by the interstitial cells of Cajal. Although the gastrointestinal tract is the most common location, there have also been reports of GISTs originating in the omentum and peritoneum. This case is a 60 year old white male who presented with weight loss and abdominal pain. Evaluation revealed a hepatic mass encompassing much of the right lobe of the liver. A biopsy of the mass contained spindle elements in a fibrous stroma, which stained positive for CD117. Furthermore, a serum α-fetoprotein level, gastroscopy, colonoscopy, small bowel enteroclysis, and bone scan were normal. The patient was started on Gleevec (tyrosine kinase inhibitor), but after three months developed pulmonary lesions/malignant pleural effusions and ultimately died of cardiorespiratory failure. As mentioned before, although GISTs have been reported to originate in the omentum and peritoneum, this is a case of a primary hepatic GIST. More importantly, this novel location emphasizes the current understanding regarding the origin of these tumors. Specifically, these tumors might be comprised of a heterogenous group in respect to the cell of origin, cellular differentiation, and prognosis. In addition, GISTs may arise from the pluripotent stem cell, which gives rise to the interstitial cell of Cajal. This is based on the fact that both cells express CD117. The only approved treatment for non-resectable GISTs is Gleevec (imatinib mesylate), which is a tyrosine kinase inhibitor. Although initial studies show some promise, the long-term outcomes are currently being studied.
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