Breast Cancer Patients’ Cognitive Functioning Before and After Chemotherapy: A Systematic Review and Meta-analysis

Introduction: With improvements in treatment, a growing number of breast cancer patients survive their primary cancer and require counseling from their general practitioner (GP) on how to handle long-term side-effects of treatment. Many breast cancer patients experience cognitive problems following chemotherapy which interfere with their abilities to fulfill social and work-related responsibilities. However, since the cause of the cognitive problems is unknown, it is difficult for GPs to offer appropriate counseling on this issue. Aim: To conduct a systematic review and meta-analysis of the available evidence concerning cognitive functioning of breast cancer patients before and after chemotherapy. Methods: The databases PubMed and SSCI were searched for articles on the cognitive functioning of breast cancer patients receiving chemotherapy. The search took place from August to December 2010 and extended as far back as the databases allowed. Seven studies were selected based on three inclusion criteria: prospective studies, use of neuropsychological tests and inclusion of two patient groups: one receiving chemotherapy and one not receiving chemotherapy (control group). Results: At baseline, breast cancer patients who were to receive chemotherapy scored higher on executive function than the controls (effect size (ES)=-0.202, p=0.011), but significantly lower on overall cognitive functioning as well as on the specific domains of attention, working memory, verbal learning and memory, motor function, visual learning and memory and visuospatial function (ES=0.248 to 0.407, p=0.000 to 0.010). Post-treatment, the patients who had received chemotherapy continued to score significantly lower than the controls on overall cognitive functioning and on the same specific domains as before treatment (ES=0.189 to 0.430, p=0.000 to 0.038), but the between-group difference was reduced. The chemotherapy-treated patients also scored significantly lower on processing speed (ES=0.195, p=0.014) and there was no longer a difference between the groups with regards to executive function (ES=-0.109, p=0.173) and attention (ES=0.225, p=0.055). Discussion/conclusions: Breast cancer patients who received chemotherapy scored significantly lower on neuropsychological tests after chemotherapy than patients who did not receive chemotherapy. This difference was, however, also evident before chemotherapy, suggesting that other factors than chemotherapy may play a role. Chemotherapy-treated breast cancer patients are characterized by having more advanced stages of disease which are again associated with increased levels of cytokines and more emotional distress. Whether these factors are responsible for the cognitive problems observed in breast cancer patients remains a question for future research. The results will be of importance to GPs offering guidance on the long-term side-effects of cancer treatment.