A 62-year-old Caucasian male with a subepithelial gastric mass on endoscopy; FNA shows a KIT+ and DOG1+ profile. Which immunostains confirm this diagnosis?

• A. CD117+, DOG1+
• B. CD34-, PAX8+
• C. CK7+, CK20-
• D. Calcitonin+, TTF-1

Answer: (A)

Immunohistochemical profiling for a gastric subepithelial tumor relies on the typical fingerprint of a GIST. The hallmark is expression of KIT (CD117) together with DOG1. When both are positive, it strongly points to a gastrointestinal stromal tumor, especially in the stomach, and helps distinguish it from other mesenchymal or epithelial tumors. DOG1 is particularly useful because it remains a sensitive marker even in some KIT-negative cases, reinforcing the diagnosis when KIT is also positive. In contrast, the other markers would steer you toward different tumor types: calcitonin and TTF-1 suggest thyroid or lung neuroendocrine tumors; CK7/CK20 patterns and PAX8 positivity align with various carcinomas or renal/thyroid-origin tumors, not GIST. So the combination of CD117 and DOG1 positivity best confirms a GIST in this scenario.