The effect of variable mtDNA content on poor survival of laryngeal cancer patients. The lower and upper limit (4.02 and 5.42 copies) of the overall 95% confidence interval for all control subjects (A) and the relative mean mtDNA copy number (4.72 copies) of all control subjects (B) were set as the cutoff points, respectively. Kaplan-Meier analysis of survival was then performed according to copy number variations of mtDNA in a large cohort of laryngeal cancers. The results showed that both low and high mtDNA content were not associated with overall survival of the patients. However, when the data were stratified further based on the TNM tumor stage, low mtDNA content was strongly associated with worse survival in the patients who had early-stage tumors, but not in those with late-stage tumors. H, high mtDNA content; M, medium mtDNA content (or reference); L, low mtDNA content.