Multiomic characterization to reveal a distinct molecular landscape in young-onset pancreatic cancer.
Authors: Ogobuiro Ifeanyichukwu , Baca Yasmine , Walker Phillip , Wilson Gregory , Gulhati Pat , Marshall John , Shroff Rachna T. , Oberley Matthew James , Snyder Rebecca A , Parikh Alexander A. , Abbott Daniel , Kim Hong Jin , Maithel Shishir K. , Kooby David A. , Ahmad Syed , Hosein Peter Joel , Merchant Nipun B. , Korn W. Michael , Spetzler David , Datta Jashodeep 
Published: January 2022

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Background: Young-onset pancreatic cancer (YOPC; < 50 years at diagnosis) has been associated with male preponderance, extensive smoking history, and a trend towards improved survival compared with average-onset pancreatic cancer (AOPC; ≥70 years). However, the genomic and transcriptomic correlates underlying these clinical differences are incompletely understood. Using a large matched genomic-transcriptomic next-generation sequencing (NGS) dataset, we sought to characterize the distinct molecular landscape associated with YOPC compared with AOPC. Methods: A total of 2430 pancreatic ductal adenocarcinoma NGS samples (YOPC n = 292; AOPC n = 2138) with matched whole-transcriptome (NovaSeq) and DNA (NextSeq, 592-gene or NovaSeq, whole-exome) sequencing data were analyzed (Caris Life Sciences, Phoenix, AZ). Immune deconvolution was performed using the QuantiSeq pipeline. Limited clinical data precluded stage- and treatment-stratified comparisons between cohorts. Overall survival (OS) was obtained from insurance claims, and Kaplan-Meier estimates were calculated for age- and molecularly-defined cohorts. Significance was determined as FDR-corrected P-values (Q) < 0.05. Results: Of 2430 PDAC patients undergoing NGS, YOPC patients (median age 46 years) were more likely to be male (65% vs. 52%; P < 0.001) and current smokers (32% vs. 11%; P = 0.02) compared with AOPC patients (median age 75 years). YOPC patients had higher proportions of mismatch repair-deficient (MMR)/MSI-H (2.8% vs. 0.8%, P = 0.001), BRCA2-mutant (4.7% vs 2.1%, P = 0.009), and PALB2-mutant (1.4% vs 0.5%, P = 0.04) tumors compared with AOPC patients, while tumors in AOPC patients had more frequent SMAD4 (20.1% vs. 14.7%, P = 0.03), RNF43 (6.3% vs. 2.5%, P = 0.012), CDKN2A (24.8% vs. 19.2%, P = 0.04), and SF3B1 (2.7% vs. 0.7%, P = 0.04) mutations. YOPC patients also demonstrated lower HLA-DPA1 homozygosity (55.2% vs. 64.1%, Q < 0.05) vs. AOPC patients. Notably, YOPC patients demonstrated significantly lower incidence of KRAS-mutant (81.3% vs. 90.9%, Q < 0.01) tumors compared with AOPC patients. In the KRAS-wildtype subset (n = 225), YOPC tumors were more likely to be driven by NRG1 and MET fusions, while BRAF fusions were exclusively observed in AOPC patients. Computationally inferred immune deconvolution revealed enrichment of NK cell (Q = 0.04) and M2 macrophages (Q = 0.01) populations in YOPC tumors. There was an association with improved OS in YOPC patients with KRAS-wildtype (median 22.4 [YOPC- KRASWT] vs. 15.1 [AOPC- KRASWT] months, P = 0.02) but not KRAS-mutant (P = 0.28), tumors compared with AOPC patients. Conclusions: In this large real-world multi-omic characterization of age-stratified molecular differences in PDAC, YOPC is associated with a distinct molecular landscape compared with AOPC. These data reveal molecular features of YOPC with prognostic and therapeutic implications.