SDHB and gastrointestinal stromal tumor: Around 10% of cases do not harbor a KIT or PDGFRA mutation and have historically been referred to as “wild type.” A significant number (around 40% of GIST cases that lack KIT or PDGFRA mutations) have loss-of-function mutations in the succinate dehydrogenase (SDH) subunits or loss of SDH complex iron sulfur subunit B (SDHB) protein expression and are referred to as SDH-deficient GIST [15].