Cognitive Impairment Associated with Chemotherapy: Neuroimmunological Interactions, Gut–Brain Axis, and Therapeutic Approaches

Chemotherapy is a treatment designed to contain or eradicate neoplastic cells; however, patients may experience various treatment-related adverse effects. Chemotherapy-related cognitive impairment (CRCI), clinically referred to as “chemobrain,” is a frequent complication with a duration ranging from months to years, affecting between 17% and 70% of cancer patients. These cognitive deficits not only impair social, educational, and occupational functioning but may also impact survival outcomes, possibly by interfering with medication adherence and health-related behaviors. Emerging evidence has converged on an integrative cascade in which chemotherapy-induced systemic inflammation, intestinal dysbiosis, blood–brain barrier disruption, microglial/astroglial activation, and impaired hippocampal neurogenesis act in sequence rather than as independent pathways. Underlying pathophysiological mechanisms include neuroinflammation, reduced neurogenesis, loss of dendritic spines, oxidative stress, hormonal changes, epigenetic modifications, and mitochondrial dysfunction. In contrast, repair mechanisms involve complex glial responses, particularly those of astrocytes and microglia. Emerging studies suggest a link between changes in the microbiome and cognitive decline, demonstrating the importance of bidirectional communication in the gut–brain axis. Current research seeks to determine appropriate tests to identify chemobrain. Therefore, several biomarkers, such as GFAP, S100β, and isoprostanes, have been proposed to assess chemobrain, alongside screening tools such as MoCA, MMSE, and CAB-CF, to evaluate cognitive impairment and enable early detection. Pharmacological candidates—including lithium, fluoxetine, methylphenidate, modafinil, metformin, agomelatine, and melatonin—as well as nutritional and lifestyle interventions such as physical exercise, omega-3 fatty acids, curcumin, probiotics, and traditional Chinese medicine formulations—have been investigated, predominantly in animal models. These remain candidate, not validated, therapies; clinical evidence in CRCI populations is limited, heterogeneous, or absent, and well-powered randomized controlled trials are required before any recommendation can be issued. However, optimal strategies for symptom improvement remain unclear, as various approaches have yielded mixed outcomes. This review provides a comprehensive overview of chemobrain, focusing on its molecular mechanisms, interactions with the gut–brain axis, and potential therapeutic targets to improve the quality of life for cancer survivors.