Abstract 6198: Genetic analysis of synchronous or metachronous multiple pancreatic cancers
Authors: Hirano Tomonori , Kakiuchi Nobuyuki , Yasuhide Takeuchi , Nishimura Tomomi , Masui Toshihiko , Nagai Kazuyuki , Anazawa Takayuki , Minamiguchi Sachiko , Haga Hironori , Uza Norimitsu , Seno Hiroshi , Kodama Yuzo , Masuda Atsuhiro , Tanaka Takeshi , Shiraishi Yuichi , Miyano Satoru , Ogawa Seishi 
Published: June 2022

Abstract
[Introduction] The majority of patients with pancreatic cancer are inoperable at the time of diagnosis and even those cases with successful tumor resection for early-stage tumors frequently had second tumors within the remaining pancreas shortly after the surgery, contributing to a poor clinical outcome. Moreover, synchronous multiple pancreatic cancers were often reported. One of the long-standing issues about such synchronous and/or metachronous multiple pancreatic cancers is their clonal origins. In this study, we aimed to reveal the origin of multiple pancreatic cancers using an unbiased detection of somatic mutations in primary and metachronous cancers as well as adjacent precursor lesions.
[Methods] Serially obtained formalin-fixed paraffin-embedded surgical specimens from 17 patients who had undergone curative surgery for an early-stage pancreatic cancer were subjected to laser microdissection for the enrichment of tumor and precancerous lesions, from which DNA was extracted and analyzed for somatic mutations using whole-exome sequencing (WES) with matched normal DNA. Based on shared and private mutations across different samples, we interrogated history of clonal evolution of these lesions.
[Results] We analyzed 17 patients with multiple pancreatic cancers of 2 metachronous and synchronous, 10 metachronous, and 2 synchronous tumors. In metachronous cases, pathology for primary cancer were margin-negative in all patients, and the median interval between the initial and second surgery was 37.7 months (12 - 85 months). In addition, we analyzed 5 adjacent pancreatic intraepithelial neoplasia (PanIN) in one of these cases. We identified a median of 66 (range: 31-232) and 20 (14-42) somatic mutations in cancer and PanIN lesions, respectively. None of the patients have known pathogenic germline variants. All samples had one or more driver mutations. In most cases (N=16), sharing many somatic mutations, multiple tumors had a common clonal origin. In another synchronous case, the synchronous tumors shared only one mutation, suggesting that they were clonally independent tumors. By contrast, none of the mutations other than hotspot KRAS mutations were shared between precursor and cancer lesions. While multiple independent clones were observed in precancerous lesions, most of multiple cancers originated from a common ancestor. Moreover, negative pathology of the margins at the initial surgery suggested that those multiple lesions arose from distant dissemination or metastasis, rather than contiguous, intraductal invasion.
[Conclusions] In conclusion, our study suggests that even early pancreatic cancer might be disseminated within the pancreas and contribute to synchronous and metachronous cancers.
Citation Format: Tomonori Hirano, Nobuyuki Kakiuchi, Takeuchi Yasuhide, Tomomi Nishimura, Toshihiko Masui, Kazuyuki Nagai, Takayuki Anazawa, Sachiko Minamiguchi, Hironori Haga, Norimitsu Uza, Hiroshi Seno, Yuzo Kodama, Atsuhiro Masuda, Takeshi Tanaka, Yuichi Shiraishi, Satoru Miyano, Seishi Ogawa. Genetic analysis of synchronous or metachronous multiple pancreatic cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 6198.