Non-cancer-related Deaths in Cancer Survivors: A Nationwide Population-based Study in Japan

BACKGROUND: Advancements in cancer care have improved survivorship, potentially leading to changes in mortality causes. This study aimed to investigate the causes of death among cancer survivors, specially focusing on non-cancer-related mortality. METHODS: This nationwide population-based cohort study analyzed the causes of death based on the time since cancer diagnosis using data from the National Cancer Registry in Japan between January 2016 and December 2019. Non-cancer-related deaths were identified, and mortality risks associated with non-cancer diseases were compared to those of the Japanese general population using standardized mortality ratios (SMRs) with 95% confidence intervals (CIs). The follow-up period was up to 4 years after cancer diagnosis. RESULTS: A total of 3,990,661 patients (45.8% women) were included in the analysis, yielding 6,237,269 person-years of follow-up. Of these, 1,001,857 (25.1%) patients died during the study period. Cancer-related and non-cancer-related causes accounted for 86.6% and 13.4% of deaths, respectively. The proportion of non-cancer-related deaths increased from 10.2% at 6 months to 31.6% at 4 years after cancer diagnosis. Heart disease (21.8%), cerebrovascular disease (9.8%), and pneumonia (9.1%) were the leading cause of non-cancer-related deaths: the SMRs for these diseases were 2.69 (95% CI, 2.66-2.72), 2.07 (95% CI, 2.03-2.10), and 2.41 (95% CI, 2.36-2.45), respectively. The SMR for suicide was 1.81 (95% CI, 1.74-1.89); however, it lost significance in males and females 2 and 2.5 years after cancer diagnosis, respectively. CONCLUSION: The proportion of non-cancer-related deaths among cancer patients has increased over time, emphasizing the need to manage cancer and its comorbidities carefully.