Psycho-Oncology Psycho-Oncology 18: 134–143 (2009) Published online 12 June 2008 in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/pon.1379 Cognitive effects of chemotherapy in post-menopausal breast cancer patients 1 year after treatment Barbara Collins 1Ã , Joyce Mackenzie 1 , Angela Stewart 2 , Catherine Bielajew 2 and Shailendra Verma 3 1 The Ottawa Hospital—Civic Campus, Ottawa, Ont., Canada 2 University of Ottawa, School of Psychology, Ottawa, Ont., Canada 3 The Ottawa Hospital Regional Cancer Centre, Ottawa, Ont., Canada Abstract Objective: Studies in breast cancer patients indicate that chemotherapy may cause subtle cognitive disturbances in some women, but the course is unclear. The current study evaluated the cognitive effects of adjuvant chemotherapy in post-menopausal breast cancer patients 1 year following completion of treatment. Patients and methods: Breast cancer patients scheduled to receive adjuvant chemotherapy (n 5 53) completed comprehensive neuropsychological testing before commencing chemother- apy (T1), 1 month after completing chemotherapy (T2), and again 1 year later (T3). A control group of women receiving adjuvant hormonal therapy (n 5 40) was tested at comparable intervals. A standardized regression-based approach was used to identify cognitive decline, and incidence of decline was compared across treatment groups. Results: Whereas at T2, chemotherapy patients were more likely to show cognitive decline than hormonal patients, by T3, the frequency of reliable cognitive decline was the same in both groups (11 and 10%, respectively). However, those chemotherapy patients receiving hormonal therapy at T3 were inferior to the chemotherapy patients not receiving hormonal treatment on composite measures of processing speed and verbal memory. Conclusion: These data suggest that there is a subtle negative impact of chemotherapy on cognitive function in breast cancer patients shortly following completion of treatment, but that this resolves within 1 year. However, given that our control group comprises breast cancer patients receiving hormonal therapy, and indications that hormonal therapy may also adversely affect cognition, such conclusions must be considered tentative. Copyright r 2008 John Wiley & Sons, Ltd. Keywords: breast cancer; oncology; adjuvant chemotherapy; cognitive function; adjuvant hormonal therapy Introduction Due to great advancements in the detection and treatment of breast cancer, there is a growing survivorship and an increasing emphasis on the long-term adverse effects of cancer treatments. Many breast cancer patients complain of poor concentration and memory, and muddled, ineffi- cient, and effortful thought processes [1]—a condi- tion known in patient circles as chemo fog or chemo brain. As cognition has indisputable and important implications for quality of life, there has been a burgeoning of research on this topic over the last several years. The preponderance of studies investigating this phenomenon in the breast cancer population has found poorer neuropsychological performance in chemotherapy-treated patients than in control subjects [2–17]. However, most of these studies were retrospective in nature and many of them compared the chemotherapy-treated patients with healthy individuals without cancer. It is now well established that cancer patients are at increased risk for cognitive compromise, whether or not they have received chemotherapy [18–25]. Retrospective studies do not allow us to conclude that observed cognitive disturbances were not present prior to treatment. Moreover, reliance on a healthy control group does not control for a myriad of potentially confounding host- and disease-related factors that could account for incident cognitive decline in cancer patients. These methodological shortcomings led to a call for studies that included pretreatment testing of cognition, as well as a disease-specific comparison group not receiving chemotherapy. The study that we report on here is one of only a handful of controlled prospective studies of cognitive function in breast cancer patients, and one of even fewer studies to include a treatment group with more * Correspondence to: The Ottawa Hospital—Civic Campus, 1053 Carling Avenue, Room A603, Ottawa, Ont., Canada K1Y 4E9. E-mail: bcollins@ ottawahospital.on.ca Received: 10 October 2007 Revised: 7 March 2008 Accepted: 15 March 2008 Copyright r 2008 John Wiley & Sons, Ltd.