Identification of sequence polymorphism in the D-loop region of mitochondrial DNA as a risk factor for breast cancer.

Mitochondrial DNA (mtDNA) variations affect the efficiency of the electron transport chain and production of reactive oxygen species, contributing to carcinogenesis. The D-loop region of mtDNA has emerged as a variation hotspot region in human neoplasia; however, the potential contribution of these variations in breast cancer risk prediction remains unknown. We investigated the relationship between germline single nucleotide polymorphisms (SNPs) in the entire D-loop region and breast cancer risk in Chinese women. Peripheral blood-isolated mtDNA from 2329 patients with breast cancer and 2328 cancer-free controls was examined for SNPs. In the combined cohort, we used traditional risk factors, susceptibility germline polymorphisms, and logistic regression analysis to evaluate the predictive value of susceptibility variants for breast cancer risk. We calculated the area under the receiver operating characteristic curve (AUC) as a measure. We also measured the content of 8-hydroxy-2'-deoxyguanosine (8-OHdG). Individual polymorphisms SNP573 were significantly associated with breast cancer risk in both the discovery and validation cohorts. In the combined cohort, the AUC of the traditional risk factors was 64.3%; after adding susceptibility variants, the AUC was 64.9% (DeLong test, p = 0.007). 8-OHdG levels were significantly higher in patients with breast cancer than in controls and higher in individuals with SNP573 than in those negative for this variation. Overall, oxidative stress might be associated with the risk of breast cancer, and SNP573 might be associated with oxidative stress. Our results indicate the risk potential of polymorphisms in the D-loop region in breast cancer in Southern China.