The impact of circulating free tumor DNA (cfDNA) in testicular germ cell tumors (TGCT) management.

Abstract

e17519 Background: The clinical management of testicular germ cell tumors (TGCT) has not changed much for decades; most importantly, novel prognostic factors indicating the need of adjuvant chemotherapy and factors related to the development of cisplatin resistance would be needed. Circulating free tumor DNA (cfDNA) is an easily available and valuable source of genetic material, which may bring clinically relevant information. Methods: After ethical committee approval and patient informed consent, peripheral blood (PB) samples were taken from TGCT patients at the diagnosis (after orchidectomy), after 2 cycles of chemotherapy, at the end of treatment, and at relapse or disease progression, if applicable. Clinical data of all patients were recorded. The PB samples were processed immediately after collection, plasma was separated by centrifugation, cfDNA was extracted by QIAmp Circulating Nucleic Acid kits (Qiagen), its quality and quantity was assessed by capillary electrophoresis (Agilent) and qPCR for a house-keeping gene. Selected samples were subjected to whole exome sequencing using SureSelectXT HS + Human All Exon v6 kits (Agilent) on NextSeq (Illumina) platform, together with the corresponding primary testicular tumor and peripheral blood mononuclears as a germ-line control. Statistical analyses were performed using non-parametric tests. Results: Sixty-three samples of 41 patients have been analyzed. The median amount of detected cfDNA did not significantly differ from non-malignant controls, was similar in seminoma and non-seminoma pts, but was significantly higher (p = 0.01) in pts with disease progression. In pts with elevated cfDNA levels, these decreased after 2 and 4 cycles of chemotherapy. In 5 sequenced pts, molecular aberrations (somatic missense or frameshift mutations) were found in genes CDC27 (2 pts), RBMX (4 pts), TPTE2 (3 pts), and TSPAN16 (1 pt). These aberrations were also detected in primary tumors but with lower frequencies, and were not present in germ-line DNA. CDC27 mutations have been described in TGCT previously. The other genes have not yet been linked to TGCT, although their role in spermatogenesis and cell proliferation is well known. The presence of mitochondrial DNA was not detected in cfDNA. Conclusions: High levels of cfDNA are detectable in pts with disease progression where they reflect the total tumor load; the molecular analysis of cfDNA revealed novel aberrations that may play a role in TGCT development. Supported by grants MH CZ - DRO00064190TN, CDRO00064203FNM and MEYS NPU I LO1604