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The present study aimed to investigate gene mutations in the displacement‑loop (D‑loop) region of mitochondrial DNA (mtDNA) in patients with oral squamous cell carcinoma (OSCC) in order to examine the role of gene mutation in mtDNA in OSCC tumorigenesis. mtDNA was obtained from cancer tissues, paracancerous tissues and normal mucosal tissues of thirty patients with OSCC. The D‑loop region of the mtDNA was amplified using polymerase chain reaction, sequenced and then analyzed by Chromas software and BLAST to identify the mutation sites. Mutations in the D‑loop region were observed in the cancer tissue samples of eight out of thirty cases with OSCC, with a mutation rate of 27%. There were nine mutations in total, including one point mutation, two base deletions, three insertion mutations and three heterozygous mutations. In these mutations, base deletions were different from each other and heterozygous mutations did not have the same mutation form; however, the three insertion mutations were the same, consisting of an insertion of a C base. One case contained a T/A heterozygous mutation as well as base insertion of C. The eight cases with mutations in the D‑loop region consisted of three cases of tongue cancer, two cases of soft palate cancer, one case of floor of the mouth cancer, one case of oropharyngeal cancer and one case of lip cancer. This study demonstrated mutations in the mtDNA D‑loop region in OSCC cells; however, the association between occurrences of OSCC and mtDNA mutations requires further investigation.

Objective: To investigate the gene mutation in D-loop region of mitochondrial DNA (mtDNA) in oral squamous cell carcinoma (OSCC) tissue and to explore the role of the gene mutation in D-loop region in the OSCC tumorigenesis., Methods: mtDNA was obtained from cancer, paracancerous and normal mucosa tissues of thirty patients with OSCC. The D-loop regions of mtDNA were amplified with PCR, sequencing and then analyzed by Chromas software and BLAST to identify the mutation site., Results: Mutation in the D-loop region was found in eight cases, with the mutation rate of 27%. There were nine mutations totally, including one point mutation, two base deletions, three insertion mutations, three heterozygous mutations. In these mutations, base deletions were different from each other and heterozygous mutations had no same mutation form, while the three insertion mutations were same, the insertion of base C. One case had T/A heterozygous mutation and base C insertion at the same time., Conclusions: There were mutations in mtDNA D-loop in OSCC, but the relationship between occurrence of OSCC and mutation of mtDNA needs further study.

Objective: To investigate the frequency of mitochondrial DNA (mtDNA) D-loop hypervariable region II (HVR II) and hypervariable region III (HVR III) mutations in oral squamous cell carcinoma (OSCC) and their correlation to provide the new targets for the prevention and treatment of OSCC., Methods: The D-loop HVR II and HVR III regions of mtDNA in seven cases with OSCC tissues, matched with paracancerous tissues and normal mucosa tissues from the same case, were amplified by polymerase chain raction (PCR), then were detected by direct sequencing to find the mutantsites after the comparison of all sequencing results with the mtDNA Cambridge sequence in the GenBank database., Results: 82 (56 species) nucleotide changes, with 51(26 species) nucleotide polymorphism, were found after the comparison of all sequencing results with the mtDNA Cambridge sequence in the GenBank database. 31(30 species) mutations, with 21 located within the HVR II and HVR III regions, were found in 3 tumor tissue samples, their paracancerous and normal mucosa tissue were found more polymorphic changes but no mutation. The mtDNA D-loop HVR II and HVR III regions mutation rate was 42.9% (3/7) in OSCC., Conclusion: The mtDNA D-loop HVR II and HVR III regions were highly polymorphic and mutable regions in OSCC. It suggested that the D-loop HVR II and HVR III regions of mtDNA might play a significant role in the tumorigenesis of OSCC. It may become new targets for the gene therapy of OSCC by regulating the above indexes.