Association of mtDNA copy number with clinicopathological variables in laryngeal cancer. Copy number of mtDNA was analyzed using real-time quantitative PCR approach. Details are as described in Methods. (A) A frequency distribution of the number of cases by mtDNA copy number, age, and pack-years. (B) The relationship of mtDNA copy number with various clinical features of laryngeal cancer patients. The circle represents mtDNA copy number of each case of laryngeal cancers. Horizonal lines represent mean ± S.E. Sample means were compared using the Mann–Whitney U test. F, female; M, male; Well, well/moderate differentiation; Poor, poor/undifferentiation; N, non-lymph node metastasis; Y, lymph node metastasis.