Fifteen-year survival and conditional survival of women with breast cancer in Osaka, Japan: A population-based study

Background: In recent years, the survival of patients with breast cancer has improved. However, few published studies have a longer than 10-year follow-up. Conditional relative survival (CRS), which is relative survival (RS) of patients who have survived beyond a certain period after diagnosis, is useful for assessing excess mortality among long-term survivors compared with the general population.

Methods: This was a retrospective observational cohort study. Population-based cancer registry data in Osaka, Japan were used to determine 15-year RS and 5-year CRS of women with breast cancer diagnosed between 2001 and 2002 and followed up for at least 15 years. Fifteen-year RS and age-standardized RS (ASR) were calculated by Ederer II and cohort methods. Five-year CRS according to age group and extent of disease (localized, regional, and distant) was estimated for every year from diagnosis to 10 years.

Results: In the cohort of 4006 patients, the ASR declined progressively, the 5-year ASR being 85.8%, 10-year ASR 77.3%, and 15-year ASR 71.6%. The overall 5-year CRS exceeded 90% at 5 years after diagnosis, reflecting a small excess mortality compared with the general population. The 5-year CRS of patients with regional and distant disease did not reach 90% within 10 years of follow-up (89.4% for regional and 72.9% for distant disease 10 years after diagnosis), indicating that these patients had substantial excess mortality.

Conclusion: Long-term survival data can help cancer survivors plan their lives and receive better medical care and support.