Finland, a northern European country, has a population of approximately 5.6 million people and a population density that is among the lowest in Europe (Fig. 1).1 For both men and women in Finland, lung cancer (LC) is the third most common type of cancer, with the highest cancer mortality rate among men and the second highest among women.2 Finland’s age pyramid reflects a greater proportion of older individuals. As of 2021, LC constituted 8.1% of all cancer cases in the nation.2

The aim of this study was to validate the discriminatory ability and clinical utility of the N descriptor of the newly proposed ninth edition of the TNM staging system for lung cancer in a large independent cohort.

Estonia, a European Union (EU) member since 2004, is located in Northern Europe, sharing a mainland border with Russia and Latvia and a maritime border with Finland and Sweden (Fig. 1). Estonia has a population of about 1.37 million, rapidly aging during the past decade.1 In 2022, the life expectancy at birth was 74 years for men and 82 years for women—one of the biggest gender gaps in the EU.2 In the same year, approximately half of the deaths in Estonia were caused by cardiovascular diseases (47%), closely followed by cancers (40%).