Effect of ctDNA whole-exome sequencing in pancreatic adenocarcinoma on prognostic value, actionable alterations, and organ tropisms in metastatic disease.

4149 Background: The dismal prognosis associated with pancreatic ductal adenocarcinoma (PDAC) needs a deeper understanding of progression mechanisms and personalized treatment. While the prognostic value of ctDNA has already been established, this study purposes to apply plasma whole-exome sequencing (WES) to identify molecular alterations beyond KRAS. This approach aims to predict survival, uncover progression mechanisms, and identify therapeutic targets. Methods: Eighty metastatic PDAC patients were prospectively recruited and divided into two consecutive cohorts: discovery (n=37) and validation (n=43). Tumor and plasma obtained at diagnosis were analyzed using WES. The variant allele frequency (VAF) of KRASmutations was quantified by ddPCR in plasma at baseline and at response from all patients (n=80). Results: Plasma WES identified at least one pathogenic variant across all individuals, which can be categorized into four pathways: oncogenic mechanisms, DNA repair, microsatellite instability and TGFb pathway alterations. 7 unique druggable mutations were detected in tissue and 11 in plasma. Other targetable mutations ( CDK12, NF1, BRCA2, and TSC2), were prevalent in plasma but absent in tissue. Patients with survival less than 11 months showed enrichment in cellular organization pathways and exclusive targetable CDK12 mutations. Longer survival cases exhibited exclusive mutations in DNA regulation and repair genes. Patients with liver metastasis displayed unique mutations not just in KRAS but also in the adaptive immune response pathway genes. Baseline plasma KRAS mutations detected by ddPCR was associated with worse progression-free survival. (HR=2.315, CI 95%= 1.027-5.217, p = 0.038; and HR= 3.022, CI 95% = 1.299 - 7.030, p= 0.007 in the discovery and validation cohort, respectively). A significant risk of progression (p = 0.006) was observed if KRAS VAF at response assessment did not decrease, at least, 84.75% in both cohorts. Conclusions: ctDNA WES unveils molecular signatures of rapid progression, potential actionable alterations, and liver metastasis-specific mutations in the adaptive immune response pathway. KRAS detection at baseline and its evolution during treatment emerge as prognostic biomarkers. Table: see text