Assessment of cell-free DNA (cfDNA) as a biomarker in pancreatico-biliary malignancies: A longitudinal observational cohort study.

e16480 Background: Globally, cfDNA and circulating tumor DNA (ct-DNA) are gaining recognition in Pancreaticobiliary malignancies for prognostic evaluation and MRD assessment. However, data on cfDNA from India remains limited. We aimed to quantify baseline cfDNA and understand the association of their clinicopathological features and survival with cfDNA and its dynamics. Methods: We recruited 36 patients with newly diagnosed Pancreaticobiliary malignancies (PDAC = 7, GBC = 29). Cohort A had patients with curative intent (n = 9), while Cohort B included patients with palliative intent (n = 27). 5ml blood was collected in EDTA tubes at 2 time points: baseline (Sample 1) and post-therapy (Sample 2). Sample 2 was collected either at the end of neoadjuvant therapy or 24 hours post-surgery in cohort A. In cohort B, sample -2 was collected after 3 months of first-line therapy. cfDNA was isolated using the Maxwell-RSC-ccfDNA isolation kit and quantified using SYBR-Green real-time-PCR of the beta-globin gene. No intervention was planned on cfDNA levels. Results: Baseline characteristics of all 36 patients are shown in Table 1. Mean baseline cfDNA levels were higher in GBC as compared to PDAC (1.79±5.71 ng/ul vs 1.16±1.03 ng/ul respectively, p = NS). No significant association was observed between TNM stage, node positivity, histology, CA 19.9, and baseline cfDNA levels. Baseline cfDNA levels did not show a significant association with clinical response, progression-free survival (PFS), or overall survival (OS). Longitudinal samples (1 and 2) were available for 7 patients (GBC). We found fair concordance between cfDNA dynamics (rise or fall) & clinical response. cfDNA responders had a trend toward improved PFS & OS (p = NS). Conclusions: There was no significant association between Baseline cfDNA and the clinicopathological profile in both PDAC and GBC. However, cfDNA dynamics were concordant with clinical response in GBC. Baseline characteristics (total no of patients=36). Characteristics n (%) Age (years) Median (IQR) 51 (45–59) Gender Males 13 (36.1%) Females 23 (63.9%) TNM Stage I-III 10 (27.8%) IV 26 (72.2%) Tumor (T) Stage T1-T2 7 (19.5%) T3-T4 29 (80.5%) Node (N) Stage Node negative 14 (38.9%) Node positive 22 (61.1%) Histology Well-differentiated 13 (36.1%) Moderately differentiated 15 (41.7%) Poorly differentiated 8 (22.2%) Her2 Expression (GBC) 8 (22%) CA 19.9 (u/ml) Median (IQR) 71.5 (13.2–688.5)