Objective and subjective cognitive impairment following chemotherapy for cancer: A systematic review

Evidence suggests that some cancer survivors experience cognitive difficulties following chemotherapy. However, perceived or subjective cognitive impairment is more frequently reported than prevalence revealed by objective assessments. The aim of this review was to examine the relationship between subjective and objective measures of cognitive impairment following treatment for cancer and to determine the number of studies that found a significant relationship between these measures of cognition. A comprehensive search for articles, published between 1980 and 2012, comparing subjective and objective cognition in cancer patients treated with chemotherapy was conducted. Of 818 potentially relevant articles, 23 studies met the inclusion criteria for the current review and one article was sourced from reference lists of included studies. Only eight of 24 included studies found a significant relationship between objective and subjective measures of cognitive performance. These studies were more likely to involve breast cancer patients and to assess the relationship between memory and perceived cognitive impairment. The failure to consistently find an association between subjective and objective measures of cognition could be explained by variations in assessment methods or the definition of impairment. Alternatively, objective and perceived cognitive impairment may be unrelated because perceived impairment may be an indicator of psychological distress rather than cognitive impairment. Despite these discrepancies, patients' perceptions of impairment are important due to its significant impact on quality of life. Further research is required to explore whether objective measures of everyday functioning better predict the impact of chemotherapy related cognitive impairment on daily functioning.