We show that proportionally, twice as many mitochondrial genes are common essential genes when compared to the genome as a whole. Under hypoxia, loss of mitochondrial genes, including OXPHOS genes such as succinate dehydrogenase subunit C (SDHC), improves the growth of U2OS cells, as well as HeLa and MCF7 cells, and downregulated expression of OXPHOS proteins is an intrinsic response of tumour cells to hypoxia. This evidence concerns the gene SDHC and neoplasm.