This study tested 2 hypotheses: (1) chemotherapy increases the rate of cognitive decline in breast and colorectal cancer patients beyond what is typical of normal aging and (2) chemotherapy results in systematic cognitive declines when compared with breast and colorectal cancer patients who did not receive chemotherapy.
Data came from personal interviews with a prospective cohort of patients with breast (n=141) or colorectal cancer (n=224) with incident disease drawn from the nationally representative Health and Retirement Study (1998–2006) with linked Medicare claims.
The 27-point modified Telephone Interview for Cognitive Status was used to assess cognitive functioning, focusing on memory and attention. We defined the smallest clinically significant change as 0.4 points per year.
We used Bayesian hierarchical linear models to test the hypotheses, adjusting for multiple possible confounders. Eighty-eight patients were treated with chemotherapy; 277 were not. The mean age at diagnosis was 75.5. Patients were followed for a median of 3.1 years after diagnosis, with a range of 0 to 8.3 years. We found no differences in the rates of cognitive decline before and after diagnosis for patients who received chemotherapy in adjusted models (P=0.86, one-sided 95% posterior intervals lower bound: 0.09 worse after chemotherapy), where patients served as their own controls. Moreover, the rate of cognitive decline after diagnosis did not differ between patients who had chemotherapy and those who did not (P=0.84, one-sided 95% posterior intervals lower bound: 0.11 worse for chemotherapy group in adjusted model).
There was no evidence of cognitive decline associated with chemotherapy in this sample of older adults with breast and colorectal cancer.
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*Department of Health Sciences, School of Health Professions
†Department of Psychological Sciences, College of Arts and Science, University of Missouri, Columbia, MO
‡Department of Internal Medicine, University of Michigan Medical School
§Veterans Affairs Health Services Research and Development Center of Excellence
∥Institute for Social Research, University of Michigan, Ann Arbor, MI
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Supported by NIH grants K08 HL091249, R01 AG027010, and R01 AG030155, the Society of Critical Care Medicine’s 2010 Vision Grant, and by pilot support from the Michigan Institute for Clinical and Health Research (MICHR), UL1RR024986. The National Institute on Aging provides funding for the Health and Retirement Study (U01 AG09740), which is performed at the Institute for Social Research, University of Michigan.
The authors declare no conflict of interest.
Reprints: Victoria A. Shaffer, PhD, Department of Health Sciences, School of Health Professions, Department of Psychological Science, College of Arts and Science, University of Missouri, 504 Clark Hall, Columbia, MO 65221-4290. E-mail: firstname.lastname@example.org.