Real-time polymerase chain reaction analysis of a 3895-bp mitochondrial DNA deletion in epithelial swabs and its use as a quantitative marker for sunlight exposure in human skin.

BACKGROUND: The use of mitochondrial DNA (mtDNA) damage as a reliable and highly sensitive biomarker of ultraviolet (UV) radiation exposure in both the dermis and epidermis has now been well developed by our group and others. We have previously identified a 3895-bp mtDNA deletion which occurred more frequently and to a higher level in usually sun-exposed skin as opposed to occasionally sun-exposed skin. This work focused on older-aged individuals and, in particular, perilesional, histologically normal skin biopsies taken from patients with skin cancer. OBJECTIVES: To develop novel, less-invasive methods of obtaining skin samples (i.e. epidermis) from volunteers covering a much wider age range and larger number of individuals (n = 239). METHODS: The 3895-bp deletion was quantified by a specific real-time polymerase chain reaction assay in normal human epidermis samples taken from three body sites with differing sun exposure. RESULTS: The results show a statistical increase of the level of the 3895-bp deletion with increasing sun exposure in the epidermal swabs of human skin (P < 0·001) and with increasing age of the donor in the needle biopsy samples. CONCLUSIONS: These data suggest that the upper layers of the epidermis are an accessible and reliable site for assessing mtDNA damage caused by UV exposure.

Accurate prediction of repeat prostate biopsy outcomes by a mitochondrial DNA deletion assay.

Several cancers are characterized by large-scale mtDNA deletions. We previously provided evidence that one of these deletions has potential utility in resolving false from true-negative prostate needle biopsies. This study was to assess the clinical value of this deletion in predicting re-biopsy outcomes. We used a quantitative polymerase chain reaction assay to measure the levels of the deletion in individual negative needle biopsies from 101 patients who had a repeat biopsy within a year with known outcomes. Using an empirically established cycle threshold (Ct) cutoff of 31, and the lowest Ct for each patient as diagnostic of prostate cancer, as well as the histopathologic diagnosis on second biopsy, we calculated the clinical performance of the deletion. The Ct cutoff at 31 gave a sensitivity and specificity of 84 and 54%, respectively, with the area under a receiver-operating characteristics curve of 0.749. The negative predictive value was 91%. The assay was able to predict the presence of a missed tumor in 17 out of 20 men a year before diagnosis. This ancillary test appears to identify men who do not require a repeat biopsy with a high degree of certainty. The results suggest that the majority of men with atypical small acinar proliferation have a concurrent missed tumor and therefore require close monitoring for early detection.