Describe the histology of a gastrointestinal stromal tumor (GIST).

Describe the histology of a gastrointestinal stromal tumor (GIST).

• A. Spindle or epithelioid cells with smooth muscle differentiation
• B. Gland-forming malignant cells with desmoplastic stroma
• C. Squamous differentiation with keratinization
• D. Spindle or epithelioid cells with CD117 (c-KIT) and DOG1; originates from interstitial cells of Cajal

Answer: (D)

GISTs are mesenchymal tumors of the GI tract that arise from interstitial cells of Cajal in the wall of the bowel. Histologically, they are composed of spindle-shaped cells (the most common pattern) or epithelioid cells arranged in fascicles or sheets. The defining immunophenotype is strong positivity for CD117 (c-KIT) and DOG1, with many also expressing CD34; this profile distinguishes GISTs from true smooth muscle tumors and carcinomas. The origin from interstitial cells of Cajal explains KIT signaling mutations that drive growth, and KIT-targeted therapy (imatinib) is a key treatment for unresectable or metastatic cases. The other descriptions fit different tumor types (smooth muscle differentiation, gland-forming carcinomas, or keratinizing squamous cell carcinomas) and do not capture the classic GIST histology and immunoprofile.

GISTs are mesenchymal tumors of the GI tract that arise from interstitial cells of Cajal in the wall of the bowel. Histologically, they are composed of spindle-shaped cells (the most common pattern) or epithelioid cells arranged in fascicles or sheets. The defining immunophenotype is strong positivity for CD117 (c-KIT) and DOG1, with many also expressing CD34; this profile distinguishes GISTs from true smooth muscle tumors and carcinomas. The origin from interstitial cells of Cajal explains KIT signaling mutations that drive growth, and KIT-targeted therapy (imatinib) is a key treatment for unresectable or metastatic cases. The other descriptions fit different tumor types (smooth muscle differentiation, gland-forming carcinomas, or keratinizing squamous cell carcinomas) and do not capture the classic GIST histology and immunoprofile.