Post-Diagnosis Depression and Suicide Risk Among Cancer Survivors: A Nationwide Population-Based Cohort Study

Patients with cancer are at increased risk of suicide, but the contribution of depression arising after cancer diagnosis remains poorly characterised.

To evaluate whether first-recorded depression after cancer diagnosis was associated with subsequent suicide risk among adults with cancer who had no documented depression before cancer diagnosis.

Using the South Korean National Health Insurance Service database. 755,079 adults newly diagnosed with cancer between 2009 and 2013, without documented depression before cancer diagnosis, were followed through 2023. Depression after cancer diagnosis was defined using ICD-10 codes and modelled as a time-dependent exposure, and suicide was identified from national mortality records. The primary analysis used cause-specific Cox regression to estimate adjusted hazard ratios (aHRs); Fine-Gray regression was used as a complementary analysis accounting for non-suicide death as a competing event.

During a median follow-up of 13.0 years, 1926 deaths by suicide occurred. Suicide incidence rates were higher among patients with post-diagnosis depression than among those without depression (47.0 vs. 17.7 per 100,000 person-years). In multivariable time-dependent Cox models, post-diagnosis depression was associated with a substantially increased risk of suicide (aHR 4.76, 95% confidence interval [CI] 4.28-5.28). The association was stronger among patients younger than 60 years and among women (both p for interaction < 0.001).

Depression arising after cancer diagnosis was strongly associated with suicide risk in this nationwide cohort and represents a clinically relevant marker of suicide risk among cancer survivors, supporting the integration of systematic mental health assessment into routine oncology care.