Circulating cell-free DNA-based biomarkers for prognostication and disease monitoring in adrenocortical carcinoma.

Adrenocortical carcinoma (ACC) is a rare aggressive cancer with heterogeneous behaviour. Disease surveillance relies on frequent imaging, which comes with significant radiation exposure. The aim of the study was to investigate the role of circulating cell-free DNA (ccfDNA)-related biomarkers (BM) for prognostication and monitoring of ACC. We investigated 34 patients with ACC and 23 healthy subjects (HS) as controls. ccfDNA was extracted by commercial kits and ccfDNA concentrations quantified by fluorimeter (BM1). Targeted sequencing was performed using a customised panel of 27 ACC-specific genes. Leucocyte DNA was used to discriminate somatic variants (BM2), while tumour DNA was sequenced in 22/34 cases for comparison. Serial ccfDNA samples were collected during follow-up in 19 ACC patients (median period 9 months) and analysed in relationship with standard radiological imaging. ccfDNA concentrations were higher in ACC than HS (mean±SD, 1.15±1.56 vs 0.05±0.05 ng/µl, P<0.0001), 96% of them being above the cut-off of 0.146 ng/µl (mean HS+2SD, positive BM1). At ccfDNA sequencing, 47% of ACC showed at least one somatic mutation (positive BM2). A combined ccfDNA-BM score was strongly associated with both progression-free and overall survival (HR=2.63, 95%CI=1.13-6.13, P=0.010, and HR=5.98, 95%CI=2.29-15.6, P=0.0001, respectively). During disease monitoring, positive BM2 showed the best specificity (100%) and sensitivity (67%) to detect ACC recurrence or progress compared to BM1. In conclusion, ccfDNA-related BMs are frequently detected in ACC patients and represent a promising, minimally invasive tool to predict clinical outcome and complement surveillance imaging. Our findings will be validated in a larger cohort of ACCs with long-term follow-up.