SDHB and gastrointestinal stromal tumor: Heterozygous germline mutations in SDH complex (SDHx) genes (SDHA, SDHB, SDHC, SDHD, and SDHAF2), which act as tumor suppressor genes, predispose to pheochromocytomas and paragangliomas (PPGLs) and rarely to gastrointestinal stromal tumors (GIST), renal cell carcinoma, and pituitary adenomas.