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Background This study aimed to compare treatment strategies and survival of patients with synchronous colorectal peritoneal metastases (CPM) and patients with metachronous CPM in a nationwide cohort. Methods All patients from the Netherlands Cancer Registry with synchronous or metachronous CPM whose primary colorectal cancer (CRC) was diagnosed between 1 January and 30 June 2015 were included in the study. Treatments were categorized as (A) cytoreductive surgery and hyperthermic intraperitoneal chemotherapy [CRS-HIPEC]; (B) palliative treatment; or (C) best supportive care. Overall survival (OS) for all the patients and disease-free survival (DFS) for those who underwent CRS-HIPEC were compared between the two groups. Results Of 7233 patients, 743 had a diagnosis of CPM, including 409 patients with synchronous CPM and 334 patients with metachronous CPM. The median OS was 8.1 months for the patients with synchronous CPM versus 12 months for the patients with metachronous CPM (p = 0.003). After multivariable correction, OS no longer differed between the patients with synchronous CPM and those with metachronous CPM (HR 1.03 [0.83–1.27]). The patients with metachronous CPM more often underwent CRS-HIPEC than the patients with synchronous CPM (16 % vs 8 %; p = 0.001). The two groups did not differ statistically in terms of DFS and OS (median DFS, 21.5 vs 14.1 months, respectively; p = 0.094; median OS, 37.8 vs. 35.8 months, respectively; p = 0.553). Conclusion This population-based study showed that survival for the patients with synchronous CPM and patients with metachronous CPM did not significantly differ. This suggests that a similar prognosis may be expected for patients selected for treatment regardless of the onset of CPM.

The peritoneum is a common metastatic site in gastric cancer. This systematic review provides an overview of the incidence, risk factors and survival of synchronous peritoneal metastases from gastric cancer. A systematic search was performed to identify studies wherein the incidence, risk factors and survival of gastric cancer with peritoneal metastases were investigated. Of all 38 potentially eligible studies, 17 studies were included based on the eligibility criteria. The incidence of synchronous gastric peritoneal metastases was reviewed for population-based studies (10–21%), for observational cohort studies (2–15%) and for surgical cohort studies (13–40%). Potential risk factors for synchronous gastric peritoneal metastases were younger age, non-cardia gastric cancer, female sex, signet ring cell carcinoma, diffuse type histology or linitis plastica, T4 stage, Hispanic ethnicity and more than one metastatic location. Synchronous peritoneal metastases are commonly diagnosed in patients with gastric cancer with an incidence up to 21% in recent population-based studies. Furthermore, prognosis of patients with gastric peritoneal metastases is poor with median overall survival ranging from 2 to 9 months. The high incidence and poor prognosis require intensive research on diagnostic features and effective treatment options to improve survival.

The aim of the study was to gain insight in the incidence, treatment, and survival of patients with synchronous pancreatic peritoneal metastases.Methods: All patients diagnosed with pancreatic cancer between 2008 and 2018 in the Netherlands Cancer Registry were evaluated. The patients were subcategorized as (1) synchronous peritoneal metastases, (2) synchronous systemic metastases, and (3) no metastases.Results: In total, 25,334 patients with pancreatic cancer were included.Among them, 3524 (14%) presented with synchronous peritoneal metastases, 10,659 (42%) with systemic metastases, and 11,151 (44%) without metastases at the time of diagnosis. The proportion of the patients diagnosed with peritoneal metastases increased over time (11%, 2008; 16%, 2018; P < 0.001). Of these patients, 964 (27%) received cancer treatment and 2560 (73%) received best supportive care. The median overall survival in patients with peritoneal metastases, systemic metastases, and without metastases was 1.9, 2.4, and 8.0 months, respectively (P < 0.001). In the patients with peritoneal metastases, the median overall survival was 5.0 months when undergoing cancer treatment and 1.3 months with best supportive care (P < 0.001).Conclusions: Patients with pancreatic cancer are increasingly diagnosed with synchronous peritoneal metastases. Given the current dismal prognosis, research to improve treatment is designated for this patient category.