Exploring depression risk among breast cancer survivors: A nationwide cohort study in South Korea.

19 Background: With advances in early diagnosis and treatment, the population of breast cancer survivors globally continues to grow. Depression among these survivors poses a significant concern for their long-term survivorship and overall quality of life. This study aims to investigate the incidence of depression among breast cancer survivors and identify associated risk factors. Methods: We used the National Health Insurance Service database of Korea from 2010 to 2016 and examined 59,340 breast cancer survivors and 1:2 age-matched individuals without breast cancer to investigate the incidence of depression. Cox proportional hazards regression was used to calculate the hazard ratio (HR) and 95% confidence interval (CI). The risk of depression was assessed based on age, categorizing individuals as under or over 50 years old. We conducted 1-year, 3-year, and 5-year lag sensitivity analysis to demonstrate changes in risk over time. The study identified risk factors for developing depression through multivariable Cox regression, and Kaplan-Meier analysis was conducted to illustrate the incidence probabilities of depression in breast cancer survivors. Results: Breast cancer survivors exhibited a 39% increased risk of depression compared to individuals without breast cancer, and those under the age of 50 years facing higher risk than their older counterparts (HR 1.64, 95% CI 1.58-1.70 and HR 1.23, 95% CI 1.20-1.27, respectively). Chemotherapy (anthracycline and taxane) and endocrine therapy (tamoxifen and aromatase inhibitor) emerged as potential risk factors for depression among breast cancer survivors. Sensitivity analysis revealed a decreasing trend in depression risk over time, particularly among survivors aged older than 50 years. Conclusions: This study highlights a significant increase in depression risk among breast cancer survivors, particularly those under 50 years old. Specific treatments such as chemotherapy and endocrine therapy were identified as potential risk factors. These findings emphasize the necessity for targeted interventions and support strategies to address the heightened risk of depression in breast cancer survivors, ultimately improving their long-term well-being and quality of life.