Purpose: There is evidence that some cancer survivors suffer cognitive impairment after chemotherapy. Determining if a patient has cognitive impairment is challenging, especially because impairment is usually subtle.
Patients and methods: We assessed the design of studies evaluating cognitive function during or after chemotherapy in adult patients with solid tumors. We also reviewed methods used to evaluate cognitive function in subjects with other diseases and make recommendations for future studies.
Results: We identified 22 studies that met our criteria: 82% included women with breast cancer. Eight studies were longitudinal, 12 were cross-sectional, and two were follow-ups of cross-sectional studies. Sixteen studies used a battery of neuropsychological (NP) tests to assess subjects, and 13 included a control group. Ten studies (45%) had no explicit definition of cognitive impairment; most others used z scores or T scores and defined impairment based on standard deviations below the mean, but there was no consistency in for the cutoff point used or the number of tests required.
Conclusion: There is no consistency in defining cognitive impairment, in the NP batteries used, or in statistical methods in studies of cognitive function of cancer patients. We suggest guidelines to define criteria for cognitive impairment. Use of summary scores and control groups is recommended. Practice effect should be adjusted for in longitudinal studies. A balance is needed between comprehensive batteries and briefer tests, which still need to be sensitive to mild impairment.