Low copy number of mitochondrial DNA (mtDNA) predicts worse prognosis in early-stage laryngeal cancer patients

Objectives: Alterations in mitochondrial DNA (mtDNA) copy number have been widely reported in various human cancers, and been considered to be an important hallmark of cancers. However, little is known about the value of copy number variations of mtDNA in the prognostic evaluation of laryngeal cancer. Design and methods: Using real-time quantitative PCR method, we investigated mtDNA copy number in a cohort of laryngeal cancers (n = 204) and normal laryngeal tissues (n = 40), and explored the association of variable mtDNA copy number with clinical outcomes of laryngeal cancer patients. Results: Our data showed that the relative mean mtDNA content was higher in the laryngeal cancer patients (11.91 +/- 4.35 copies) than the control subjects (4.72 +/- 0.70 copies). Moreover, we found that mtDNA content was negatively associated with cigarette smoking (pack-years), tumor invasion, and TNM stage. Notably, variable mtDNA content did not affect overall survival of laryngeal cancer patients. However, when the patients were categorized into early-stage and late-stage tumor groups according to TNM stage, we found that low mtDNA content was strongly associated with poor survival in the former, but not in the latter. Conclusions: The present study demonstrated that low mtDNA content was strongly correlated with some of clinicopathological characteristics, such as cigarette smoking, tumor invasion and TNM stage. In addition, we found a strong link between low mtDNA content and worse survival of the patients with early-stage tumors. Taken together, low copy number of mtDNA may be a useful poor prognostic factor for early-stage laryngeal cancer patients.