The impact of an open or laparoscopic approach on the development of metachronous peritoneal metastases after primary resection of colorectal cancer: results from a population-based cohort study

Background: This study aimed to assess the impact of open or laparoscopic resection of primary colorectal cancer (CRC) on the development of metachronous colorectal peritoneal metastases (CPM) in a population-based cohort. Materials and methods: This was a retrospective, population-based study of CRC patients who underwent open or laparoscopic resection of the primary tumour in the Netherlands between January 1st and June 30th 2015. Patients with synchronous metastases were excluded. CPM were considered metachronous if diagnosed ≥ 90 days after resection of primary CRC. Multivariable cox regression analysis was performed to correct for tumour location, histology, differentiation, and stage, nodal stage, tumour perforation, primary surgery type, and unclear resection margins. Results: In total, 1516 CRC patients underwent open resection and 3236 CRC patients underwent laparoscopic resection, with a 3-year cumulative incidence of metachronous CPM of 7.3% and 3.7%, respectively (p < 0.001), after median follow-up of 42 months. Open surgical approach was significantly associated with the development of metachronous CPM: HR 1.4 [95%CI 1.1–1.8]. Other prognostic factors were mucinous adenocarcinoma histology (HR 1.6, 95%CI 1.0–2.5), T4 stage (HR 3.2, 95%CI 2.3–4.5), N1 stage (HR 2.9, 95%CI 2.1–4.0), and N2 stage (HR 4.2, 95%CI 2.9–6.1). Conclusions: Patients treated with open resection had a significantly higher risk to develop metachronous CPM than patients treated with laparoscopic resection. The mechanisms underlying this phenomenon remain unknown but might be related to differences in per-operative specimen handling, tumour spill, surgical trauma and pro-inflammatory response. This finding might imply the need for a personalized follow-up after primary resection of CRC.