Depression and long-term mortality among 5-year breast cancer survivors in Korea: a retrospective population-based cohort study.

To examine the association of depression after breast cancer diagnosis with long-term mortality risk in a Korean cohort. We conducted a retrospective population-based cohort study using data from the National Health Insurance Service (NHIS) cancer patient’s cohort of South Korea. We included women aged 40 years or older who were diagnosed with breast cancer between 2007 and 2013, survived at least 5 years, and had no history of depression prior to the breast cancer diagnosis. Depression was defined as hospitalization for more than 2 days with a primary diagnosis of depression (ICD-10 codes F32–F33). We evaluated all-cause, cancer-specific, and non-cancer-specific mortality using the Cox proportional hazards model while adjusting for covariates. Among 30,873 eligible women (mean age, 56.5 years), 502 were diagnosed with new-onset depression during the 5-year survival period, whereas 30,371 did not develop depression. During follow-up after the 5-year survivor period, a total of 1,904 deaths occurred. New-onset depression was associated with higher risks of all-cause mortality (adjusted hazard ratio [aHR], 1.38; 95% CI, 1.03–1.86; p = 0.033) and non-cancer mortality (aHR, 1.81; 95% CI, 1.14–2.86; p = 0.011), while no significant association was observed for cancer-specific mortality. The association was particularly pronounced among patients aged 65 years or older (aHR, 1.96; 95% CI, 1.27–3.03; p = 0.002). Depression was linked to increased mortality among 5-year breast cancer survivors, especially for non-cancer causes. This study implies the need for depression screening and treatment among breast cancer patients, especially in non-Western settings where depression may be underdiagnosed and undertreated.