Conditional survival in breast cancer up to 10 years in the Nordic countries.

Background: Survival in breast cancer (BC) has developed favorably but late recurrences are still a problem.

Methods: We model survival data from the NORDCAN database and analyze 1-, 5-, and 10-year relative survival and 5/1- and 10/5-year conditional survival in BC from Denmark (DK), Finland (FI), Norway (NO), and Sweden (SE) between 1971 and 2020. Conditional survival measures survival in those who had survived year 1 to reach year 5 (5/1), or in those who had survived year 5 to reach year 10 (10/5).

Results: Almost all survival metrics were best for SE but survival in all countries improved in the course of time approaching the SE levels which were 98.3% for 1-year, 92.3% for 5-year, and 87.8% for 10-year survival. Conditional 10/5-year survival, covering 5 years, was better than 5/1-year survival, covering 4 years. A contributing factor is most likely the high rate of recurrence in period 2-5 years. The difference was observed for all countries but for DK 10/5-year survival approached 1-year survival and for NO and SE 10/5-year survival was only barely better than 5/1-year survival. The explanation to this was the excellent 10/5-year survival in DK compared to SE and particularly to NO. Literature search suggested that the reason for the relatively low 10/5-year survival in NO might be stagnant survival development in old patients.

Conclusions: We assume that late mortality is critically limiting survival in BC and either interference with the late metastatic process or effective treatment will be key to future improvements in BC survival.