A new study has reported that women undergoing chemotherapy experience varying degrees of cognitive impairment ("chemo brain") based on their age and cognitive reserve at the start of treatment. Cognitive reserve refers to the difference between the cognitive performance predicted by an individual's level of brain pathology or injury and that individual's actual performance. In other words, those whose measured cognitive performance is better than predicted have high reserve, whereas those who perform worse than predicted have low reserve.

The study included 60 breast cancer patients who received chemotherapy (average age 51.7 years), 72 breast cancer patients not exposed to chemotherapy (56.6 years), and 45 healthy controls (52.9 years). The women treated with chemotherapy were evaluated with a battery of neuropsychological and psychological tests before chemotherapy and at one, six and 18 months after treatment. The other two groups were evaluated at matched intervals.

Chemotherapy was found to reduce processing speed and verbal ability. Processing speed refers to the ability to automatically and fluently perform relatively easy or routine cognitive tasks, especially when high mental efficiency (i.e., attention and focused concentration) is required. Older patients with lower baseline cognitive reserve who received chemotherapy had lower performance on processing speed tests compared to both breast cancer patients not exposed to chemotherapy and cancer-free women. The verbal ability scores of the chemotherapy group had not improved as of one month after treatment but did improve as of the six- and 18-month follow-up assessments. Additional analyses also suggested that tamoxifen had a negative impact on processing speed and verbal memory in the breast cancer patients who did not receive chemotherapy. The authors conclude that age and pretreatment cognitive reserve were related to post-treatment decline in processing speed in women exposed to chemotherapy. In addition, chemotherapy had a short-term negative impact on verbal ability. Preliminary analysis of the influence of tamoxifen suggests that this pattern of results may be due to a combination of chemotherapy and tamoxifen.