Structural brain alterations following adult non-CNS cancers: a systematic review of the neuroimaging literature.

Cancer and cancer treatments may impact the brain through several pathways leading to cognitive impairment. Neuroimaging evidence has begun to elucidate the neurobiological underpinnings of cancer-related cognitive impairment. The aim of this paper was to systematically review available literature on structural brain alterations following adult non-central nervous system (CNS) cancers and associated treatments. This review followed PRISMA guidelines and was registered in PROSPERO (ID#107387). Comprehensive searches were conducted in June 2018 using PubMed and Web of Science. Inclusion criteria were English peer-reviewed journal articles of formal, controlled studies that examined structural neuroimaging outcomes in adult non-CNS cancer patients and survivors. Selected articles were assessed for quality and risk of bias using the National Institutes of Health Quality Assessment Tool for Observational Cohort and Cross-Sectional Studies. Thirty-six publications of prospective and cross-sectional studies met inclusion criteria and were included. Structural brain alterations following cancer and its treatment were reported in a majority of the publications as evidenced by reduced global and local gray matter volumes, impaired white matter microstructural integrity, and brain network alterations. Structural alterations were most often evident when cancer-treated groups were compared with healthy controls, and more subtle when compared with cancer controls. Regarding the existence of pretreatment impairments, the evidence was equivocal. There was significant between-study heterogeneity in imaging analytical approaches and use of statistical adjustments. Over half reported associations with cognitive outcomes, though regions and associated cognitive domains were heterogeneous. Structural brain alterations following cancer and cancer treatments were reported in a majority of the reviewed studies. However, the extent of observed alterations depended on the choice of comparison groups. Methodological issues exist that will need to be addressed systematically to ensure the validity of findings. Large-scale prospective studies with extended assessment points are warranted to replicate and build upon initial findings.