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

## TL;DR

This study examines survival rates and recurrence risks among cancer survivors in Japan who are enrolled in private cancer insurance.

## Contribution

The study provides age- and sex-specific survival estimates and recurrence risks using a private insurance database in Japan.

## Key findings

- Five-year relative survival declines with age, with lower rates for older males and females.
- Survivors of liver cancer had the highest recurrence rates, even after five cancer-free years.
- Conditional survival improved over time for most groups, exceeding 90% for many survivors.

## Abstract

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.

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.

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.

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.

The online version contains supplementary material available at 10.1007/s10147-025-02871-6.