Factors behind favorable long-term lung cancer survival in Norway compared to Denmark: a retrospective cohort study

Background: Long-term survival of patients with non-small cell lung cancer (NSCLC) is considerably higher in Norway compared to Denmark, even though diagnostic work-up, treatment, and follow-up are comparable. We aim to explore factors behind favorable long-term survival for lung cancer patients in Norway compared to Denmark. Method: A retrospective cohort study of patients with NSCLC diagnosed between 2014 and 2016. From the Danish Lung Cancer Registry, 1000 patients were randomly selected, and 974 patients were included. From the Norwegian Vestfold Hospital Trust, 220 patients were randomly selected, and 218 were included. Data from medical records were obtained for all patients. The Danish and Norwegian cohorts were compared using the Pearson chi squared test and multivariate logistic regression analysis. Results: The two cohorts were comparable in terms of age, sex, and smoking history. However, the Danish patients had a higher number of pack-years (43.5 vs 34.5 p < 0.001) and more comorbidities. The Norwegian patients had less advanced disease stage (p < 0.001), and a larger proportion was treated with curative intent (90 (41.3%) vs 343 (35.2%), p = 0.063). One-year survival was similar, but the 5-year survival was superior in the Norwegian cohort (58 (26.6%) vs 177 (18.2%), p = 0.005). In a multivariate logistic regression model, adjusted for sex, smoking history, performance status, TNM stage and comorbidity, the odds ratio of being a five-year survivor in Norway was 1.81 (95% CI: 1.11–2.94) compared to Denmark. Conclusions: We found a higher proportion of Norwegian patients diagnosed at potential curable stage and fewer heavy smokers compared to Danish patients. This could contribute to the superior long-term survival found in Norwegian NSCLC patients.