Relative survival among cancer survivors enrolled in private cancer insurance in Japan, using the internal insurance-enrolled population as the reference.

Background: Limited data are available on relative survival (RS) among cancer survivors enrolled in private cancer insurance in Japan. Additionally, the incidence of second primary cancers or recurrences, as applicable, after a certain period remains unclear.

Methods: We analyzed 8,846 cancer survivors, including carcinoma in situ, aged 15-79 years, enrolled in private cancer insurance between April 2005 and September 2021, and diagnosed before April 2022. Using the entire insurance-enrolled population as the reference, we estimated sex- and age group-specific RS, conditional RS (CRS), and age-standardized RS (ASR) by cancer type. The cumulative incidence of second primary cancers or recurrences, as applicable, was calculated among cancer-free 3-, 4-, and 5-year survivors.

Results: Median ages at first diagnosis were 61.5 years for males and 55.0 years for females. Over median follow-up of 3.40 years, 1,772 deaths (45.4 per 1,000 person-years) occurred. The 5-year RS declined with age: 81.8% for males and 94.8% for females aged 15-39, but 68.5% and 71.8% for those aged 70-79. The 5-year CRS increased with time since diagnosis, exceeding 90% among 5-year survivors in all groups except males aged 70-79. Liver cancer survivors had the highest incidence of second primary cancers or recurrences, predominantly due to recurrences, even after 5 cancer-free years.

Conclusion: We estimated sex- and age group-specific RS, CRS, and ASR by cancer type, and the incidence of second primary cancers or recurrences, using a database of private cancer insurance policyholders, though the findings may not be generalizable to the national population.