Abstract 2315: Temporal changes in circulating tumor cells and circulating tumor DNA in patients with resectable pancreatic ductal adenocarcinoma

Background: Circulating tumor cells (CTCs), circulating cell-free DNA (cfDNA), and circulating tumor DNA (ctDNA) are minimally invasive biomarkers that carry vital tumor onset, progression, and metastasis information, which is crucial for cancer diagnosis, prognosis, and management. We report here our longitudinal study of these circulating biomarkers in resectable pancreatic ductal adenocarcinoma (PDAC) patients. Although the overall 5-year survival rate of PDAC is low (~6%), truly resectable patients are expected to have better outcomes than non-resectable PDAC patients, especially if liquid biopsy can help guide anticancer treatment selection. Method: We evaluated temporal changes in CTCs, cfDNA, and ctDNA in peripheral blood samples in a cohort of patients with resectable PDAC treated with pre-operative chemotherapy and surgical excision. Five PDAC survivors in complete remission for three years without evidence of disease served as negative controls. Samples of peripheral blood were collected prior to the start of treatment and every two weeks while patients underwent neoadjuvant chemotherapy, followed by surgical excision of the pancreatic tumor. CTCs were enumerated using a previously reported microfluidic device [1] that integrates immunoaffinity-based isolation with size-based filtration, while cfDNA and ctDNA were measured using quantitative polymerase chain reaction (qPCR) and droplet digital PCR (ddPCR). Results: Among the initial seven patients who have completed the treatment sequences [2], CTCs were detectable in all patients (100%) at some points during treatment, but only 50% of patients had detectable CTCs before the start of chemotherapy. Median cfDNA concentrations were comparable to those negative controls throughout treatment. Using ddPCR to analyze peripheral blood samples, KRAS mutations were detected in in 71% of patients during anticancer therapy, but only in 29% patients prior to treatment. Overall, the majority of circulating biomarkers (81% for CTCs and 91% for ctDNA) were detected in blood samples collected after the start of neoadjuvant therapy and before surgery. Conclusion: This study suggests that a longitudinal study of circulating biomarkers provides additional data compared to single-point liquid biopsy, and that biologic “release” of biomarkers due to therapy can increase detectability. -Further study is needed to determine the clinical utility of liquid biopsy for resectable PDAC patients. [1] Chen, et al., Angew. Che