B2M and kidney oncocytoma: For the analysis we selected two genes encoded by mtDNA (MT-TL1 encoding 12S rRNA and MT-RNR1 encoding tRNA-leu) and normalized them to the nuclear gene B2M. To validate the assay accuracy, we analyzed samples of renal oncocytoma - a tumor type that has been previously reported to contain a higher number of mitochondria (41).