Molecular profiling of advanced pancreatic ductal adenocarcinoma (PDAC): Role of ctDNA.

Abstract

425 Background: Molecular profiling of tumour samples and circulating tumour DNA (ctDNA) may inform treatment of advanced cancer; the role of ctDNA to predict progression-free-survival (PFS) and overall survival (OS) in advanced PDAC is not fully understood. Methods: Eligible patients: those diagnosed with advanced PDAC undergoing molecular profiling [tumour (Foundation Medicine CDx/Caris) or ctDNA (FoundationMedicine Liquid (72 cancer-related genes))]. Baseline patient characteristics and molecular profiling outcomes, including mutant allele frequency (MAF) for pathological alterations were extracted. The primary aim was to assess the impact of presence of ctDNA at time of systemic chemotherapy initiation on PFS and OS. Results: Total of 26 samples (ctDNA 18 samples and 8 tumour samples) from 25 patients diagnosed with advanced PDAC underwent molecular profiling. When the whole population was analysed, the rate of sample analysis failure seemed to be higher when tumour tissue was tested (37.5%) compared to ctDNA (5.56%); p-value 0.072. The overall rate of identification of pathological findings was 72.73%, with 18.18% of patients having targetable findings [EGFRmut (1 patient), KRAS G12C mut (1 patient), FGFR2 fusion (1 patient), RNF43 mut (1 patient)]; these findings impacted treatment management in one patient only (RNF43 mutation; Wnt inhibitor). Variants of unknown significance were identified in 63.64% of samples. Patients with ctDNA analysis at time of palliative chemotherapy initiation (16 samples; 15 patients) were analysed [6 female (40.00%), median age 69.57 years (range 51.61-81.49), metastatic disease (66.67%), 80% first-line (80%), 20% second-line]. Pathological mutations were identified in 9/15 (60.00%) of these patients (KRAS mutation identified in 6/9). After median follow-up of 8.33 months from sample acquisition, 80% and 53.33% of patients had progressed and died, respectively. Median estimated PFS and OS were 5.65 months (95% CI 1.59-8.17) and 7.80 months (95% CI 4.13-not reached). Presence (vs absence) of pathological alterations in ctDNA showed a trend towards shorter PFS (2.91 vs 6.51 months; HR 1.38 (95% CI 0.40-4.77)) and OS (6.12 vs 9.72 months; HR 2.03 (95% CI 0.60-6.82)). Conclusions: This pilot study demonstrates the feasibility of ctDNA analysis in patients with advanced PDAC prior to initiation of palliative therapy. The presence of pathological alterations in ctDNA may prognosticate for worse PFS and OS. Larger studies are required to confirm these findings.