Assessment Of Circulating Free DNA (CFDNA) and Circulating Melanoma Cells (CMCS) as Prognostic Biomarkers in Metastatic Cutaneous Melanoma

Background cfDNA is detectable in patients with metastatic cutaneous melanoma and its plasma concentration could potentially predict their clinical outcomes. We assessed the correlation between cfDNA concentration and patients' overall survival and clinical characteristics including known poor prognostic factors in melanoma. Prognostic value of CMCs number and its association with cfDNA level was also explored. Methods Pre-treatment blood samples from 50 patients with metastatic cutaneous melanoma were collected prospectively. cfDNA was extracted from 1 ml of plasma using QIAamp Circulating Nucleic Acids Kit (Qiagen, Hilden, Germany) and quantified by RNase P qPCR (ABI Life Technologies, Foster City, NJ, USA). CMC enumeration per 7.5 ml whole blood was performed within 96 hours of sample collection using the CellSearch Melanoma Kit (Veridex, NJ, USA). Correlation between cfDNA concentration and clinical characteristics and CMC number was performed using χ2-test and Fisher's exact test where appropriate. Survival curves were produced and compared by the Kaplan-Meier method and log-rank test respectively. Results The median concentration of cfDNA was 6.8 ng/ml (range 0-205.8) and median CMC number was 0/7.5ml (range 0-16). Patients with cfDNA concentration of >75% percentile had significantly shorter overall survival compared to those with cfDNA level <75% percentile (median survival 100 vs. 242 days, p = 0.01). Similarly, patients with ≥ 1 CMC/7.5ml had poorer overall survival compared to those with non-detectable CMC (median survival 111 vs. 283 days, p = 0.001). No correlation was found between cfDNA concentration and CMC number. Median cfDNA concentration was significantly correlated with LDH level (p = 0.001) but not with age, performance status, AJCC stage, period with metastatic disease, number of metastatic sites and tumour BRAF mutation status. Conclusions Plasma cfDNA concentration and presence of CMC in 7.5 ml whole blood can predict patient's survival outcomes in metastatic cutaneous melanoma. No association was found between these two biomarkers and this highlights the possibility that they may represent different tumour biological process.