Altered levels of circulating nuclear and mitochondrial DNA in patients with Papillary Thyroid Cancer

Papillary thyroid cancer is the most common thyroid cancer type. However, diagnostics based on fine needle biopsy cannot make a definitive diagnosis in 25% of thyroid nodules. Additionally, approximately 70% to 80% of thyroid lobectomies performed just for diagnostic purposes are benign. Despite this, biopsy still remains the main method of evaluation of thyroid nodules. Cell-free DNA (cf-DNA) measurement could give a new diagnostic opportunities which may reduce the number of unnecessary thyroid procedures. In this study, using a qPCR, we have examined the nuclear cf-DNA and mitochondrial cf-DNA in the plasma of 32 patients. We have found that the level of nuclear cf-DNA is almost 2-fold increased (median 3 089 vs. 1 872, p = 0.022), whereas mitochondrial cf-DNA content was significantly decreased in respect to healthy controls (median 44 992 vs. 92 220, p = 0.010). The ROC curve analysis showed high specificity for nuclear cf-DNA and mitochondrial cf-DNA, which may serve as a useful tool to decrease the number of unneeded surgeries. Our study reports the first epidemiological evidence for lower mitochondrial cf-DNA content in the patient group, what suggests that apart from nuclear cf-DNA also mitochondrial cf-DNA is affected by disease development.