Abstract 5659: Origin of synchronous or metachronous multiple pancreatic cancers
Authors: Hirano Tomonori , Kakiuchi Nobuyuki , Takeuchi Yasuhide , Anazawa Takayuki , Nagai Kazuyuki , Masui Toshihiko , Minamiguchi Sachiko , Haga Hironori , Tanaka Takeshi , Masuda Atsuhiro , Kodama Yuzo , Uza Norimitsu , Seno Hiroshi , Miyano Satoru , Tanaka Hiroko , Ogawa Seishi 
Published: March 2024

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. Additionally, synchronous multiple pancreatic cancers have been frequently documented. One of the long-standing issues about such synchronous and/or metachronous multiple pancreatic cancers is their clonal origins. This study is designed to elucidate the origin of multiple pancreatic cancers through an unbiased detection of somatic mutations in primary and metachronous cancers, along with adjacent precursor lesions.
[Methods] Serially obtained formalin-fixed paraffin-embedded surgical specimens from 20 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. The investigation into the shared and private mutations across different samples aimed to unveil the clonal evolution history of these lesions.
[Results] We analyzed 20 patients with multiple pancreatic cancers of 2 metachronous and synchronous, 16 metachronous, and 2 synchronous tumors. In metachronous cases, all patients exhibited margin-negative pathology for the primary cancer, with a median interval of 38.9 months (ranging from 7 to 85 months) between the initial and second surgery. In addition, a total of 20 pancreatic intraepithelial neoplasia (PanIN) from 5 of these cases were analyzed. 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=19), 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 in early pancreatic cancer, dissemination within the pancreas may occur, contributing to the development of synchronous and metachronous cancers.
Citation Format: Tomonori Hirano, Nobuyuki Kakiuchi, Yasuhide Takeuchi, Takayuki Anazawa, Kazuyuki Nagai, Toshihiko Masui, Sachiko Minamiguchi, Hironori Haga, Takeshi Tanaka, Atsuhiro Masuda, Yuzo Kodama, Norimitsu Uza, Hiroshi Seno, Satoru Miyano, Hiroko Tanaka, Seishi Ogawa. Origin of synchronous or metachronous multiple pancreatic cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 5659.