278 Chapter 12 The aim of this study was to identify genomic changes in primary CRC that are associated with development of PMs, which would allow early detection and personal and early patient treatment. Such a study has not been reported yet 17, 19, despite the growing attention and possibilities for the genomic analysis of cancer using, for example, next-generation sequencing (NGS) techniques with broad gene panels investigating DNA and RNA alternations. In this explorative study, we identified specific DNA/RNA alterations (via TruSight Oncology (TSO) 500 analysis) in primary colorectal T3 tumors to predict metachronous PMs after curative resection. METHODS This study was conducted in a collaboration between the Maastricht University Medical Centre (MUMC+) and Catharina Hospital Eindhoven (CZE). The study was approved by the Institutional Medical Ethics Committee from MUMC+ (nr. 2021-2888) and CZE (nr. 2021-089) and conducted according to the Declaration of Helsinki. Patients The medical records of patients who underwent curative resection between 1 January 2012 and 31 December 2021 for colorectal adenocarcinoma were retrospectively reviewed. The research team deliberately chose to include a maximum of 40 patients in this pilot study, based on clinical prediction modeling which states at least 10 persons with the event (development of PM or LM) and 10 persons without the event (no metastases within 5 years) per included variable in the prediction model to obtain sufficient power 20. Patients with T3 tumors were classified into three groups: those who had developed metachronous PMs (n = 10); those who had developed metachronous liver metastases (LM, n = 10); and those who never developed metastatic disease within 5 years after primary surgery (M0, n = 20). Patients with metachronous PMs were not allowed to be diagnosed with metachronous LMs and vice versa. As T4 tumors penetrate the surface of the visceral peritoneum and directly invade other organs or structures, the risk of spread into the peritoneal cavity is higher. Therefore, we only included T3 tumors and deliberately excluded T1 and T2 tumors to create a homogenous population. Patients with synchronous disease were excluded. Patients in the LM and PM group had no signs of metastases during resection of the primary tumor but were diagnosed with PM or LM during follow-up, at least 6 months after initial surgery. Patients in the M0 group did not develop any type of metastases during the follow-up period of at least 5 years. All in- and exclusion criteria are summarized in Table 1. Patient record files were screened, and the first 40 patients who met inclusion criteria were contacted. Informed consent was obtained from all participants. Demographics, pre-operative, operative, and follow-up data of all patients were retrospectively retrieved from medical records.
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