Pediatric Gastric GIST With SDHA Truncation Despite Retained SDHB Staining: A Case Report

Background: Loss of SDHB by immunohistochemistry (IHC) is a practical screening marker for SDH-deficient GIST. Observation: A 14-year-old boy had a gastric GIST (KIT/DOG1 positive). Next-generation sequencing identified a truncating SDHA variant (c.1401T>A, p.Cys467Ter). Notably, SDHB IHC was strongly positive despite molecular evidence of SDH deficiency. Conclusions: Retained SDHB staining does not exclude SDH-deficient GIST. When clinicopathologic features suggest SDH deficiency, comprehensive molecular testing—including germline assessment—should be pursued, even in the context of SDHB positivity, to avoid false reassurance and to inform counseling and surveillance.