Liquid biopsy for diagnosis in patients with suspected pancreatic and biliary tract cancers: PREVAIL ctDNA pilot trial.

522 Background: Most patients with pancreatic cancer (PC) and biliary tract cancer (BTC) present with advanced disease. In confirmed cases, circulating tumour DNA (ctDNA) may be detected through liquid biopsy in 80-90%. Obtaining a diagnostic biopsy can be technically challenging, require complex invasive procedures and may not be feasible due to comorbidity. Reduction in capacity of aerosol generating diagnostic procedures in many healthcare systems due to COVID19 has highlighted the unmet need for simple, non-invasive diagnostic tools. We piloted the use of ctDNA to support the diagnostic pathway in patients with suspected cancer across 6 tumour types, here we present its use in PC/BTC. Methods: This single centre prospective cohort pilot trial was conducted at the Royal Marsden from June 2020 to August 2021. 16 patients were planned each in the PC and BTC cohorts. Eligibility included radiologically suspicious PC/BTC without histological diagnosis, patients with prior non-diagnostic biopsy and inaccessible tumours. Liquid biopsy for ctDNA was collected for plasma based next generation sequencing, using a custom 59 gene panel of common variants in PC/BTC tumours, including analysis for somatic, copy number and structural variants. Clonal haematopoiesis of indeterminate potential (CHIP) and germline variants were identified and subtracted. A molecular tumour board (MTB) reviewed results for interpretation and clinical context. Primary outcome was the proportion of patients with a ctDNA result consistent with a diagnosis of malignancy following MTB discussion. Results: 32 patients with suspected PC (n= 16) and BTC (n=16) were recruited. Baseline characteristics are shown in table. ctDNA was detected in 69% and 56% of patients with suspected PC and BTC respectively. MTB discussion confirmed all variants detected were consistent with a diagnosis of malignancy. At the time of data cut off, 23 patients had a subsequent biopsy. The sensitivity and specificity of ctDNA as a diagnostic tool was 80% (90% CI 49.3-96.3) and 100% (90% CI 36.8-100) for PC respectively, and 100% (90% CI 60.7-100) and 75% (90% CI 24.9-98.7) for BTC respectively. There were 2 false negatives in the PC cohort subsequently diagnosed with PC, and 1 false positive in the BTC cohort subsequently diagnosed with oesophageal cancer. Conclusions: ctDNA can be used to support a diagnosis of cancer in patients with radiologically suspected PC/BTC. A blood first, tissue second strategy in the diagnosis of PC/BTC could improve diagnostic efficiency, speed, and add resilience to the current diagnostic pathway. Clinical trial information: NCT04566614. [Table: see text]