Influence of a nationwide colorectal cancer screening program on the incidence of synchronous colorectal peritoneal metastases

This study aims to assess the influence of colorectal cancer screening on the incidence of synchronous colorectal peritoneal metastases (CPM). Patients diagnosed with CPM between 2009 and 2022 were selected from the Netherlands Cancer Registry. Crude rates of the observed and expected CPM incidence were calculated per 100,000 individuals and compared. Expected incidence was extrapolated from the incidence in the years prior to screening invitation. In total, 9,238 patients with CPM were included. For the screen-eligible population (55-75 years), the observed CPM incidence increased from 5.1 (2009) to 7.0 before screening initiation (2013) (Annual percent change [APC] 8.2%, p = .014). Since the start of screening, the observed CPM incidence stabilized: 8.8 (2014) to 8.9 (2022) (APC -1.0%, p = .159). Within the total population, the observed CPM incidence before screening showed an increase from 3.6 (2009) to 4.0 (2013) (APC 3.4%, p = .050). Since screening, a decrease in CPM incidence was observed from 4.4 (2014) to 3.5 (2022) (APC -2.2%, p = .010). The observed and expected number of CPM differed significantly in the screen-eligible population (6,437 observed vs. 7,992 expected individuals; p < .001) and in the overall Dutch population (9,238 observed vs. 10,440 expected individuals; p < .001). In conclusion, a declining trend was observed in the incidence of CPM in the Dutch population since the start of colorectal cancer screening. The observed incidence was lower compared to the expected incidence, both in the screen-eligible population and in the overall population. These findings suggest that screening results in a decrease of patients diagnosed with CPM possibly resulting in an improved survival of colorectal cancer patients.