Because mitochondria play a central role in energy and ROS production, mtDNA is an obvious candidate for genetic susceptibility studies in cancer. In the present study, for the first time, frequencies of mtDNA haplogroups and CR polymorphisms were determined in patients with malignant melanoma. No significant difference between haplogroup frequencies of patients with melanoma and control subjects could be found. Analysis of clinical characteristics revealed that there is also no association between mtDNA haplogroups and tumor invasiveness or metastatic progression. Only when categorizing Breslow thickness did we find an association: haplogroup J was overrepresented in thick melanoma, indicating that this haplogroup might be associated with higher tumor thickness and therefore less favorable prognosis 
. However, this finding must be considered as tentative given the small sample size of patients within Breslow category 2. Therefore, further investigations should examine a higher number of melanoma cases with high values of Breslow thickness. In addition, it has to be considered that we performed a high number of statistical comparisons, which increases the possibility of obtaining significant p-values by chance.
To our knowledge, this is the first association study on melanoma and mitochondrial CR polymorphisms. To date, mutations within the D-loop are of unclear relevance, but they may influence the level of transcription and/or replication of the mitochondrial genome 
In the present study, we evaluated CR germline polymorphisms of the mtDNA of melanoma patients as possible risk factors for melanoma formation and progression, taking into account clinicopathological data.
The T16189C variant in the CR region has been associated with several other multifactorial disorders 
, including endometrial cancer 
. The T to C substitution at position 16189 frequently generates an uninterrupted poly-C tract (np 16180–16195) in the D-loop. Furthermore, this variation often leads to heteroplasmic length variation of the poly-C tract (>10 cytosines) in different mtDNA molecules of a single person 
. When the T16189C polymorphism is accompanied by a second nucleotide change, which is often the case at np 16192, the poly-C is interrupted again. Liou et al. showed that different poly-C variants showed differences in mean mtDNA copy numbers 
. Subjects with an uninterrupted poly-C had the lowest mtDNA copy number, whereas subjects harboring an interrupted poly-C showed the highest mtDNA copy number. These findings support an earlier assumption that the T16189C variant may affect mtDNA replication 
because np 16189 is very close to the termination-associated sequence of the D-loop 
. Within our melanoma cohort, the variant with the interrupted poly-C showed significantly elevated frequencies in melanoma cases compared to controls (p
0.001). We assume that this variant may alter mean mtDNA copy number also in melanoma cells. Concerning the T195C and C16270T polymorphisms, it is unclear whether these polymorphisms may be involved in tumor formation or disease progression as there are, to our knowledge, no data available showing their effect on mtDNA replication and transcription.
We further analyzed Breslow thickness of the tumor and metastasis to determine whether a certain haplogroup or CR polymorphism within the melanoma cohort correlates with tumor invasiveness or disease progression. The A302CC-insertion, which we found to be associated with a higher mean Breslow thickness, and the T310C-insertion, which was related to lower mean Breslow values, are both located within a poly-C stretch of HVR II. This C-stretch is of interest because it is involved in the formation of the persistent RNA-DNA hybrid that leads to the initiation of mtDNA heavy-strand replication 
. Therefore, alterations of this region, in analogy to the T16189C variant, might have an impact on transcription and replication of the mitochondrial genome. The T16519C substitution was found at a higher frequency in patients with malignant melanoma and metastases, indicating a potential link to disease progression. Previously, this polymorphism was found to be associated with increased breast cancer risk 
and with worse prognosis in pancreatic cancer 
In conclusion we report for the first time an association of mtDNA variations and malignant melanoma and its clinical parameters, Breslow thickness and metastasis. Therefore, genetically determined variation in mitochondrial function has to be considered, among other factors, as a potential contributor to malignant melanoma development.