Some cognitive problems in those who receive chemotherapy are more severe than in those who only receive locoregional therapy (e.g. radiation, surgery).[9, 10]
Cognitive problems with chemotherapy can negatively impact activities of daily living such as 1) work performance,
2) access to medical and other health services, 3) caring for and socially interacting with family members.
Systematic research to understand cognitive difficulties with chemotherapy was first reported during the mid 1990s to early 2000’s;[2-4, 12]
early studies often did not include pre-treatment assessment data and/or were cross-sectional in design. The lack of pre-treatment data was most likely due to difficulty obtaining such information from newly diagnosed patients. Studies over the past decade have incorporated pre-treatment assessments of cognitive function. The importance of a pre-treatment baseline was evidenced in a study
of the effects of 5-fluorouracil, doxorubicin, and cyclophosphamide (FAC) chemotherapy on cognitive function in breast cancer. This was one of the first prospective, longitudinal studies to assess cognitive function with pre-treatment and post-treatment cognitive measures. There were no overall mean differences in cognitive function between patients and controls (normative data). Within-subject analyses showed that 61% had cognitive declines in learning, attention, and processing speed. If the pre-treatment assessment had been unavailable, 46% would not have had detectable cognitive impairments (because their post-treatment assessment scores were normal). This is extremely important since cognitive dysfunction can be subtle. If a patient scores well on a cognitive test before chemotherapy and less well after treatment (but that score is still within the normal range), the decline may nevertheless represent a clinically significant difference.
Approximately ten additional longitudinal studies have investigated cancer- and/or treatment-related cognitive difficulties; many treatment studies assessed the effects of chemotherapy and used standard neuropsychological assessments.[10, 13-23]
In all, 12-82% of patients had cognitive difficulties in the domains of executive function, memory, psychomotor speed, and attention. Not all studies revealed significant changes in all domains; those in memory, executive function, processing speed, and attention appear most frequent. Additionally, many studies had small numbers and were not powered to test multiple cognitive domains. These studies utilized a variety of cognitive assessments and control groups, and most investigated patients on various treatment regimens. One recent study compared patients exposed to chemotherapy, those not exposed, and a healthy control group; those exposed to chemotherapy had the greatest deficits.
Several studies have shown cognitive deficits in cancer patients before chemotherapy.[5, 22]
For example, in one study 33% of patients had cognitive difficulties in verbal learning and memory prior to chemotherapy
. Another recent study revealed that 23% of women being treated for breast cancer had difficulty before chemotherapy.
These could be related to psychological variables related to cancer diagnosis (e.g., stress, anxiety, depression) or to other factors (e.g., cognitive reserve). More research is needed to explicitly understand factors that lead to cognitive difficulties before and during treatment, and to understand those that contribute to long-lasting impairment.
Most studies of chemotherapy-related cognitive difficulties have focused on breast cancer. Longitudinal studies are needed in other disease groups to understand whether cognitive difficulties are more or less severe in these conditions. For example, in a cross-sectional study,
breast and lymphoma patients showed long-term problems; however, no large prospective study in lymphoma has been conducted to confirm this. More work is needed in well-powered long-term observational studies to understand the course and severity of cognitive difficulties, and possible mechanisms of action.