Mitochondrial DNA (mtDNA) mutations: new insights for pancreatic cancer diagnosis and prognosis.

Introduction: The D-loop region is the major control site for mtDNA expression because it contains the reading strand for origin of replication and promoters for transcription. Somatic D-loop mutations have implicated in the pathogenesis of cancers. Our aims were to: 1) compare germline and pancreatic cancer (PC) mtDNA D-loop sequence; 2) verify whether in the germline mtDNA D-loop region there is any specific sequence correlated with PC diagnosis and outcome. Methods: Stomatic (tumor) and germline (blood) mtDNA Dloop sequence was obtained from 24 PC and from blood of 12 agematched healthy controls. mtDNA sequence was compared with the Cambridge sequence (www.mitomap.org). Results: Hot spot differences between tumor and germline mtDNA were found only in 3 patients. Among the numerous SNPs identified in our sequences, only 4 of them were unbalanced between PC and controls. These SNPs (CT16189, CT16519, AG73, CT152) were analysed by DHPLC in a larger series of patients, including 100 PC, 41 chronic pancreatitis, 87 controls and 19 pancreato-biliary tract tumors. The haplotype T at 16189 and C at 16224 was correlated with pancreatic adenocarcinoma in non smokers (X2 4.8, p 0.05), but not in smokers (X2 0.01, p: ns). In male, not in female patients with PC the mtDNA 16519 T allele was correlated with diabetes mellitus (X2 7.98, p 0.05). PC patients without distant metastases and bearing this allele survived significantly lower (Log Rank test 9.74, p 0.005). Conclusions: 1) Somatic mtDNA mutations of the D-loop occur rarely in PC. 2) T16189-C16224 haplotype enhances PC risk in the absence of cigarette carcinogens exposure. 3) mtDNA 16519 T allele favors the onset of diabetes mellitus in PC supporting the role of mitochondria in the pathogenesis of this metabolic alteration. 4) The role of this allele in worsening metabolism is probably the basis of its association with a worse prognosis in non metastatic PC.