The Landscape of Genetic Alterations Associated with Metachronous Metastasis in Patients with Pancreatic Ductal Adenocarcinoma and Its Prognostic Significance

Abstract

Metachronous metastasis is one of the major pathologic processes which significantly increases the mortality of patients with pancreatic ductal adenocarcinoma (PDA) who completed initial curative treatment. Genetic signatures that drive the metachronous mutations are not well investigated. In this study, we aimed to identify the landscape of genetic alterations associated with metachronous metastasis in patients with PDA and its prognostic significance. We retrospectively identified patients with histologically confirmed PDA who underwent next-generation sequencing using a panel of 324 pre-specified genes. The landscape of somatic mutations was stratified by metastasis types [no metastasis (nMet) vs. de novo metastasis (dMet) vs. metachronous metastasis (mMet)]. Outcomes of interest included overall survival (OS), local recurrence (LR) following radiotherapy, and association of CA 19-9 level with metastasis types. The OS was calculated using the Kaplan-Meier estimates and log-rank test, and LR was measured using cumulative incidence. A multivariate cox-regression analysis was performed to identify prognostic factors. Pathway analysis of mMet exclusive genes was performed using DAVID (Database for Annotation, Visualization, and Integrated Discovery). A total of 328 patients with PDA were included. Among them, 56 (17%), 145 (44%), and 127 (39%) patients had nMet, dMet, and mMet, respectively. The median follow up was 21.6 months (range 0.7 -136 months). The median age at the time of diagnosis was 65.5 years (range 26.77 -87.31 years). ANOVA test showed that CA 19-9 level was associated with metastasis types (p = 0.034). The median OS was 48.4 (95% CI 28.3-NA), 27.4 (95% CI 23.3-33.9), and 15 (95% CI 13.9-17.8) months for patients with nMet, mMet, and dMet, respectively (p<0.0001). The multivariate analysis (MVA) revealed that KRAS mutation (HR 2.31; 95% CI 1.37-3.9; p = 0.001), mMet (HR 0.45; 95% CI 0.34-0.61; p<0.0001), nMet (HR 0.27; 95% CI 0.16-0.45; p<0.0001), age (HR 1.01; 95% CI 1-1.02; p = 0.03), and male gender (HR 1.5; 95% CI 1.15-2.01; p = 0.002) were associated with OS. Mutations in other PDA driver genes (TP53, SAMD4, CDKN2A) were not associated with OS (p>0.05). The LR rate at 12 months post-radiotherapy was 28% and 27% for nMet and mMet, respectively (p = 0.5). Heatmap analysis identified 31 genes that were exclusively mutated in patients with mMet. These genes were enriched in pathways of transcription regulation by RNA polymerase II promoter binding, a negative regulator of apoptosis, and telomerase maintenance. This study identified metachronous metastasis-associated genetic alterations and molecular pathways. Future prospective studies incorporating whole exome sequencing are warranted to validate these findings.