Later on, the same researchers analysed saliva from 76 patients with head and neck cancer (oral cavity cancer in 54.7% of these cases) and described a reduction of mtDNA content in both mitochondrial subunit genes (cytochrome c oxidase I, Cox I; and cytochrome c oxidase II, Cox II) in comparison to pretreatment saliva. Here, MT-CO1 is linked to oral cavity cancer.