SDHB and gastrointestinal stromal tumor: The SDH succinate-to-fumarate ratio (SSFR) in the tumor has also been associated with underlying PVs in SDHx. 11Other tumors have been associated with PVs in SDHx but with much lower relative risks; these include wild-type gastrointestinal stromal tumors, SDH-deficient renal cell carcinoma, and pituitary adenomas.10