The Impact of Depression on Survival and Treatment Adherence in Cancer Patients: A Systematic Review

Depression is prevalent among cancer patients and has been proposed as a prognostic factor for survival, yet its impact across cancer types remains unclear. This systematic review evaluates the association between depression, survival outcomes, and treatment adherence in adult cancer patients. A structured search of PubMed and SpringerLink identified peer-reviewed cohort studies, meta-analyses, and narratives published between 2000 and 2025. Eligible studies included adults with histologically confirmed cancer in whom depression was assessed using clinical diagnostic criteria or validated symptom-based instruments. Outcomes of interest included overall survival (OS) and cancer-specific survival (CSS). Due to methodological heterogeneity, a narrative synthesis was utilized. Twelve studies met the inclusion criteria. Across nearly all studies, depression was associated with worse OS, with reported hazard ratios generally ranging from 1.2 to 1.8. Clinically diagnosed depression and depression occurring after cancer diagnosis were associated with stronger adverse survival effects. Persistent or severe depressive symptoms were linked to higher mortality, whereas remission of symptoms and adherence to depression treatment were associated with improved survival. In conclusion, depression is consistently associated with poorer survival in cancer patients and appears to represent a potentially modifiable prognostic factor. These findings suggest routine depression screening and integrated mental health care in oncology practice. This review was conducted following PRISMA 2020 guidelines.