WBR0246

Author	[[PageAuthor::Rim Halaby, M.D. [1] (Reviewed by Alison Leibowitz [2] and Yazan Daaboul, M.D.)]]
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Pathology
Sub Category	SubCategory::Gastrointestinal
Prompt	[[Prompt::A 62-year-old man presents to the physician's office with complaints of worsening abdominal pain over the past four months. The pain is described as dull and localized in the mid-epigastric region. The patient denies any association between his pain and food intake or posture. Upon further questioning, he describes symptoms of increasing fatigue and recent unintentional weight loss. An abdominal CT scan shows a gastric mass, and an endoscopy-guided biopsy of the mass reveals clusters of thin, elongated, spindle cells. Immunohistochemistry of this patient's tumor is most likely to reveal expression of which protein?]]
Answer A	AnswerA::C-kit
Answer A Explanation	[[AnswerAExp::Expression of C-kit is associated with GIST.]]
Answer B	AnswerB::Ret
Answer B Explanation	AnswerBExp::Expression of Ret protein is associated with multiple endocrine neoplasia (MEN) 2A and 2B syndromes.
Answer C	AnswerC::Braf
Answer C Explanation	AnswerCExp::Expression of Braf is associated with melanoma
Answer D	AnswerD::Ras
Answer D Explanation	AnswerDExp::Expression of Ras is associated with colon adenocarcinoma.
Answer E	AnswerE::C-myc
Answer E Explanation	[[AnswerEExp::Expression of C-myc is associated with Burkitt's lymphoma.]]
Right Answer	RightAnswer::A
Explanation	[[Explanation::Gastrointestinal stromal tumor (GIST) is a rare non-epithelial neoplasm of the GI tract, the mesentary, or the omentum. The majority of GIST tumors are spindle cell tumors that may be either malignant or benign. Most stromal tumors stain positively for C-Kit/CD117 (>90%), CD34, muscle-specific actin, smooth muscle actin, S-100, and desmin. Patients with GIST may be asymptomatic or have non-specific GI symptoms. This patient's symptoms of dull epigastric pain, fatigue, and weight loss, in conjunction with the CT finding of a mass in the stomach, are suggestive of malignancy. Characteristically, the pathogenesis of GIST tumors involves a gain-of-function mutation in the KIT proto-oncogene, which encodes a transmembrane receptor for stem cell factor that includes a tyrosine kinase component in its intracytoplasmic region. Educational Objective: Gastrointestinal stromal tumor (GIST) is a rare non-epithelial neoplasm of the GI tract, the mesentary, or the omentum. The majority of GIST tumors are spindle cell tumors that may be either malignant or benign. Most stromal tumors stain positively for C-Kit/CD117 References: Din OS, Woll PJ. Treatment of gastrointestinal stromal tumor: focus on imatinib mesylate. Ther Clin Risk Manag. 2008;4(1):149-62. First Aid 2014 page 232]]
Approved	Approved::Yes
Keyword	WBRKeyword::Cancer, WBRKeyword::GIST, WBRKeyword::Gastrointestinal stromal tumor, WBRKeyword::Marker, WBRKeyword::Mutation, WBRKeyword::KIT, WBRKeyword::C-kit, WBRKeyword::Proto-oncogene, WBRKeyword::Immunohistochemistry
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