BDNF and major depressive disorder: Individual risk factors included cancer types (brain, hormone-related cancers), treatment (anti-hormonal therapy, chemotherapy, cranial radiotherapy), genetic predisposition (APOE, COMT, BDNF), increasing age, comorbidities (frailty, baseline cognitive reserve, functional decline), and psychological (distress, depression, anxiety, post-traumatic stress disorder, sleeping problems, fatigue) and social factors (loneliness, caregiver support, socioeconomic status).