Potential role of circulating tumor DNA (ctDNA) in the early diagnosis and post-operative management of localised pancreatic cancer.

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4101 Background: Pancreatic cancer remains a devastating disease, with the diagnosis typically being made late. ctDNA has shown promise as a screening test for various tumor types. The detection of ctDNA post curative intent surgery has been associated with a high risk of recurrence in multiple solid tumors. We explored the potential of ctDNA to improve pancreatic cancer outcomes. Methods: Data from separate US and Australian series were combined. Plasma samples were collected prior to surgery in both studies and post-operative samples were collected in Australia from cases undergoing curative intent surgery. Clinicians were blinded to ctDNA results and adjuvant therapy was at clinician discretion. Tissue samples from both series were analyzed at Johns Hopkins University. Next generation sequencing was used to search for somatic KRAS mutations in the primary tumors and in cell-free DNA in the plasma. Clinico-pathologic, treatment and outcome data were collected. Results: 119 pts had a ctDNA sample at diagnosis (median age 67 years, 56.3% male). Sixty six pts (55.5 %) had detectable ctDNA, including 3/7 (42.9%) with stage I disease, 54/99 (54.5%) with stage II disease, 4/8 (50%) with stage III disease and 5/5 (100%) with metastases. Specific codon 12 KRAS (G12D, G12V or G12R) mutations were identified in the tumor tissue of 12/16 (75%) patients who had a ctDNA sample collected post-surgery. At a median follow-up of 15.2 months, 7/12 (58.3%) pts had recurred, including 3/8 (37.5%) with no detectable ctDNA and 4/4 (100%) with detectable ctDNA post-surgery (HR 4.9, p = 0.04). Detectable ctDNA post-surgery was significantly associated with poor overall survival (HR 6.93, p = 0.006), with a median of 8 months for pts with detectable ctDNA. Conclusions: ctDNA shows promise as a pancreatic cancer screening test, being detectable in a high proportion of pts with early stage disease. The detection of ctDNA post operatively predicts a very high risk of recurrence. The clinical utility of ctDNA to guide adjuvant therapy decision making, and its potential as a real-time marker of treatment effect, are being explored in further studies. Clinical trial information: ACTRN12612000763842.