Investigating the Trajectories of Association Between Biomarkers and Cancer-Related Cognitive Impairment in Patients...

Background/Objectives: Cancer-related cognitive impairment (CRCI) is a frequent and clinically significant consequence of breast cancer (BC) and its treatments. With rapidly evolving therapeutics and a growing body of biomarker research, a BC-specific synthesis is needed. This review aimed to evaluate associations between blood- and saliva-based biomarkers and objective and patient-reported cognitive outcomes in adults with non-metastatic BC, while accounting for treatment modality and assessment timing. Methods: This systematic review followed the Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) guidelines and was pre-registered in the International Prospective Register of Systematic Reviews (PROSPERO, ID: CRD420251079969). PubMed, Embase, and Web of Science were searched for articles published up until April 2025. Eligible studies included adults with BC that investigated associations between blood and/or saliva biomarkers and cognitive outcomes. Results: A total of 53 studies met inclusion criteria: 31 examined biochemical biomarkers; 17, genetic; and 5, both. Assessments were predominantly post-treatment. Baseline measures were more infrequent. Chemotherapy (ChT) predominated, while endocrine therapy (ET) and radiotherapy (RT) were variably examined. Targeted therapies and immunotherapies were rarely included. IL-6 and TNF-α were most consistently linked to poorer cognition, although results varied by timing and assessment type. CRP and derived indices showed intermittent associations. Stress-axis markers and BDNF were mainly related to subjective outcomes. Genetic findings implicated DNA repair and oxidative stress pathways, while APOE, COMT, and BDNF results were inconsistent. Conclusions: Evidence for biomarker correlates of CRCI in BC is highly heterogeneous. Longitudinal, harmonized, and treatment-specific studies are needed to establish reproducible biomarker panels for risk stratification and targeted intervention.