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

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

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).

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.

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.