Insomnia and elevated risk of major depressive disorder in older adult, long-term breast cancer survivors vs a matched cohort.

[STUDY OBJECTIVES] Depression frequently occurs after diagnosis of breast cancer diagnosis. This study examines the incidence of depression and whether insomnia exaggerates depression risk in long-term breast cancer survivors (BCSs).

[METHODS] A sample of 636 nondepressed females, aged 55 to 85 years, was recruited between 2015 and 2020 from a diverse community-based health plan; 315 were BCSs at least 2 years postdiagnosis, and 321 were an aged-matched comparison cohort. Both groups were stratified by the presence or absence of insomnia at baseline. The primary outcome, incident and recurrent major depressive disorder, was diagnosed over 32 months. Cox proportional hazards models estimated risk of depression (hazard ratio [HR], 95% confidence interval [CI]).

[RESULTS] A total of 310 (98.4%) BCSs, and 309 (96.3%) comparisons completed 32 months follow-up. Relative to the comparisons, risk of depression was elevated in BCSs (HR = 5.94; 95% CI = 3.34% to 10.54%, p < .001). Insomnia, as defined by the Insomnia Severity Index (>8), further increased depression risk BCS (HR = 9.91; 95% CI = 4.92% to 19.96%; p < .001), but not in the comparisons.

[CONCLUSIONS] Long-term BCSs have a heightened risk of major depressive disorder, and even subthreshold insomnia exaggerates that risk. Given that insomnia treatment can effectively prevent depression, insomnia screening and treatment have implications for depression prevention in BCSs. Statement of Significance Breast cancer survivors with insomnia show a markedly elevated risk of depression, which supports the urgent need to screen for insomnia in cancer survivors and to develop and implement insomnia treatment to prevent depression in this high-risk population.