Increase in the incidence of synchronous and metachronous peritoneal metastases in patients with colorectal cancer: A nationwide study

Introduction: - To investigate the incidence of, factors associated with, and differences between synchronous and metachronous colorectal peritoneal metastases (CPM) in a population-based cohort.

Methods: - Data from the Netherlands Cancer Registry were used. All patients diagnosed with colorectal cancer (CRC) between 1 January and June 30, 2015 were evaluated for synchronous or metachronous CPM (diagnosis ≤90 or >90 days after surgery for primary CRC), and survival in 2019 (median follow-up 38.4 months).

Results: - Of 7233 included patients, 409 (5.7%) were diagnosed with synchronous CPM. Factors associated with synchronous CPM were mucinous (OR 2.72 [1.90-3.90]) or signet ring cell (SRC) histology (OR 6.58 [3.66-11.81]), T4 (OR 4.82 [3.68-6.32]), N1 (OR 1.66 [1.20-2.30]), or N2 stage (OR 3.27 [2.36-4.52]), and synchronous systemic metastases (SM) (OR 3.13 [2.37-4.14]). After surgery for primary CRC, 326 patients developed metachronous CPM after a median time of 14.7 months (3-year cumulative incidence: 5.5%). Factors associated with metachronous CPM were younger age (HR 1.63 [1.10-2.42]), mucinous (HR 1.84 [1.20-2.82]) or SRC histology (HR 2.43 [1.11-5.32]), T4 (HR 2.77 [2.07-3.70]), N1 (HR 2.90 [2.18-3.85]), N2 (HR 3.19 [2.26-4.50]), and synchronous SM (HR 1.95 [1.43-2.66]).

Conclusion: - This population-based study found the highest incidence of CPM currently reported in literature and a strong association between the presence of synchronous SM and both synchronous and metachronous CPM. These findings may contribute to a tailored approach in the follow-up after primary CRC surgery and guide future clinical trials investigating new strategies regarding risk-reduction or early detection of metachronous CPM.