Immunohistochemistry showed concomitant loss of SDHA and SDHB expression in SDHA-mutant GIST. Complete loss of expression for SDHA (A) and SDHB was noted in the germline SDHA-mutant GIST (B), while normal liver showed preserved reactivity. In the somatic SDHA-mutant GIST there was partial loss of SDHA expression (C), while SDHB staining was absent (D). SDHA expression was retained in a WT pediatric GIST (E), while SDHB reactivity was lost (F, with internal positive control). In the control KIT exon 11-mutant GIST from a young adult both SDHA (G) and SDHB protein expressions were preserved (H).