GUSB and neoplasm: Of the 21 classical reference genes, only 3 genes (ras-related protein 7a (RAB7A), vesicle protein sorting 29 (VPS29) and glucuronidase beta (GUSB)) showed similar expression levels between tumor and normal tissues (CV < 30% and FDR > 0.05) (Additional file 1: Table S4) and thus may potentially be considered as true reference gene candidates.