SDHB and neoplasm: As previously mentioned, SDHB mutation in PCC/PGL patients is associated with an increased risk of tumor progression, and several studies have shown that SDHB gene mutations can be detected by the loss of SDHB staining by immunohistochemistry (IHC) (24, 25), we hypothesized that loss of SDHB expression in PCC/PGL tumors can function as a risk factor for progressive tumors in the current study.