Incidence of new-onset depression after colorectal cancer diagnosis and associated mortality: a population-based cohort study

Objectives: To examine the incidence of and factors associated with new-onset depression following colorectal cancer (CRC) diagnosis and its association with all-cause and CRC-specific mortality. Design: Population-based retrospective cohort study using linked administrative health databases. Setting: British Columbia, Canada. Participants: Individuals diagnosed with CRC from 2010 to 2017 without a history of physician-recorded depression diagnoses in the 5 years preceding the CRC diagnosis. Main outcome measures: New-onset depression following CRC diagnosis was identified using International Classification of Diseases (ICD)-9 and ICD-10 diagnostic codes. Cumulative incidence and incidence rates of new-onset depression were estimated, and factors associated with new-onset depression were examined using Cox proportional hazards models. Depression was modelled as a time-varying exposure in mortality analyses, with Cox proportional hazards models used to estimate hazard ratios (HR) and 95% confidence intervals (CI) for all-cause and CRC-specific mortality. Results: Among 13 986 patients with CRC (55.2% males, mean age 66.0), the 5-year cumulative incidence of new-onset depression among those without a history of depression was 6.63% following CRC diagnosis. Incidence rates were highest in the first year post-CRC diagnosis (3.54 per 100 person-years), indicating that new-onset depression was most common early after diagnosis. Factors associated with new-onset depression included female sex (HR 1.40 (95% CI 1.22 to 1.61)) and stage 4 disease (HR 1.77 (95% CI 1.34 to 2.33)). New-onset depression after CRC diagnosis was associated with 97% higher all-cause mortality (HR 1.97 (95% CI 1.74 to 2.23)) and 73% higher CRC-specific mortality (HR 1.73 (95% CI 1.48 to 2.03)). Conclusions: The cumulative incidence of new-onset depression increased over time, with incidence rates highest in the first year following CRC diagnosis. New-onset depression after CRC diagnosis was associated with higher all-cause and CRC-specific mortality. Findings highlight the importance of early identification of patients at high risk for depression and consideration of longitudinal mental healthcare in CRC care.