Clinical application of circulating cell-free DNA for monitoring the biological course of thymic epithelial tumors

8566 Background: Thymic epithelial tumors (TETs) are rare thoracic malignancies. Widely recognized as different histopathological entities, thymoma (T) and thymic carcinoma (TC), show a different biological behavior with a higher tendency to hematogenous dissemination for TC and thoracic recurrence for T, sharing, however, a poor prognosis when characterized by high tumor burden. Up to date, there are no specific biomarkers for monitoring the biological course of these rare tumors. Analysis of circulating cell-free DNA (cfDNA) has potential applications throughout the natural course of cancer development, diagnosis and treatment, never the less several studies have suggested that cfDNA levels closely parallel overall tumor burden. For the first time the detection and the correlation of cfDNA levels with tumor burden and histological subtype of TET, has been carried on in this monocentric study. Methods: Starting from July 2018, serum samples from 19 patients with TET, 4 with completely resected TET (rTET) and 15 with advanced (aTET), were prospectively obtained before the initiation of therapy. Serum samples from 15 healthy donors were used as control. Five ml of blood was collected and processed within one hour or less, followed by centrifugation at 3000g for 10 minutes and storage at -80°C. The serum samples were processed for QiAamp MinElute cell-free DNA mini kit extraction (Qiagen). cfDNA quantification was assessed using Qubit Fluorometric Quantitation (Thermo Fisher Scientific). Clinical, and histo-pathological features of TET were assessed. Results: A median cfDNA amount in healthy donors of 0.108 ng/µl (0.083-0.868) was registered. A median cfDNA of 0.512 ng/µl (0.178-1.42) resulted for the rTET, including the value of 0.178 for the resected TC. A median cfDNA of 2.53 ng/µl (1.20-6.11) resulted for the aTET, with respectively a median of 2.845 ng/µl (1.3-5.24) and of 1.5 ng/µl (1.2-6.11) for TC and T. The highest registered level for both group of thymoma (6.11 ng/µl) and thymic carcinoma (5.24 ng/µl) correlates with the highest tumor burden. Conclusions: To the best of our knowledge, this is the first study that explore detection and quantification of cfDNA in TET. Higher baseline levels than the control group and the rTET group have been registered for both advanced T and TC. Highest levels of cfDNA may be associated with high tumor burden despite the histological subtype. We envision that further valuable information will be obtained with mutational analysis.