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Background: The potential benefit of surgery of the primary tumour in patients with asymptomatic metastatic colorectal cancer is debated. This EURECCA international comparison analyses treatment strategies and overall survival in the Netherlands and Norway in patients with incurable metastatic colorectal cancer., Methods: National cohorts (2007-2013) from the Netherlands and Norway including all patients with synchronous metastatic colorectal cancer were compared on treatment strategy and overall survival. Using country as an instrumental variable, we assessed the effect of different treatment strategies on mortality in the first year., Results: Of 21,196 patients (16,144 Dutch and 5052 Norwegian), 38.6% Dutch and 51.5% (p < 0.001) Norwegian patients underwent resection of the primary tumour. In the Netherlands, 58.2% received chemotherapy compared with 21.4% in Norway. Radiotherapy was given in 9.5% of Dutch patients and 7.2% of Norwegian patients. Using the Netherlands as reference, the adjusted HR for overall survival was 0.96 (95% CI 0.93-0.99; p = 0.024). Instrumental variable analysis showed an adjusted OR of 1.00 (95% CI 0.99-1.02; p = 0.741)., Conclusions: Treatment strategies varied significantly between the Netherlands and Norway, with more surgery and less radiotherapy in Norway. Adjusted overall survival was better in Norway for all patients and patients <75 years, but not for patients ≥75 years. Instrumental variable analysis showed no benefit in one-year mortality for a treatment strategy with a higher proportion of surgery and a lower proportion of radiotherapy. Our findings emphasise the need for further research to select patients with incurable metastatic colorectal cancer for different treatment options., Competing Interests: Declaration of competing interest We declare no competing interests., (Copyright © 2020 Elsevier Ltd, BASO ~ The Association for Cancer Surgery, and the European Society of Surgical Oncology. All rights reserved.)

Several studies have shown remarkable differences in colorectal cancer survival across Europe. Most of these studies lacked information about stage and treatment. In this study we compared short-term survival as well as differences in tumour stage and treatment strategies between five European countries: Norway, Sweden, Denmark, Belgium, and the Netherlands. For this retrospective cohort study all patients aged 18 years or older and operated on adenocarcinoma of the rectum without distant metastases and diagnosed in 2008 and 2009 were selected in national audit registries from Norway, Sweden, Denmark, Belgium, and the Netherlands. Differences in pre-operative treatment between the countries were compared using univariable and multivariable logistic regression. One year relative survival and one year relative excess risk of death (RER) were compared between the five countries. Large variation in the use of preoperative radiotherapy and chemoradiation was found between the countries. Even though, there was little variation in relative survival between the countries, except Sweden, which had a significant better one year RER of death among the elderly patients after adjustment. The differences in survival are expected to be caused by differences in peri-operative care, selection of patients, and especially management of elderly patients. The effects of preoperative treatment are expected to be seen on long term follow-up., (Copyright © 2014 Elsevier Ltd. All rights reserved.)