Insight in Malignant Pleural Mesothelioma circulating DNA and possible applications in its diagnosis and treatment.

Malignant pleural mesothelioma (MPM) is a fatal tumor with a poor prognosis. The recent developments of liquid biopsies could provide novel diagnostic and prognostic tools in oncology. However, there is limited information about the feasibility of this technique for MPMs. In this work we investigated whether cancer-specific DNA sequences can be detected in pleural fluids (PF) and plasma of MPM patients as free circulating tumor DNA (ctDNA). In the second part we explore the possibility to obtain data about the mutational profile of MPM via direct sequencing of liquid biopsies samples. Performing whole-exome sequencing (WES) on tumor biopsies from various patients, we analyzed and validated patient-specific somatic mutations with digital droplet PCR (ddPCR) in PFs and plasma, using them as cancer-specific tumor biomarkers. We could show that most of the selected mutations could be detected in PFs (94%) and, noteworthy, in plasma (83%) with the use of ddPCR. PFs showed similar levels of somatically mutated ctDNA as those detected in solid biopsies with an abundances average of 22.21% and 16.3% respectively. On the other hand, the difference between ctDNA concentrations in solid biopsies and plasma was quite high, corresponding to the important drop of circulating somatically mutated DNA in the bloodstream. However, despite the amount of ctDNA the mutations were detectable at rates similar to those possible for other tumors. In the second part of the study we performed WES on samples from different patients, each presenting four different specimens: blood (BC), tumor (T), PF supernatant (S) and pellet (P). The last two were derived form PF centrifugation process. We found that there is a number of mutation common to both tumor and PF, and there is the potential to gain valid and useful information without the need for solid biopsies. In conclusion we found robust evidence that mutated DNA is spilled from MPMs, mostly into PFs, proving the concept that liquid biopsies are feasible for MPM patients. We also proved that plasma samples contain traces of tumor DNA. This work represents a good starting point to possibly change the approach to MPM treatment and ease the diagnosis and follow-up procedures.