Affiliations of authors: Department of Psychology, University of Southern California, Los Angeles, CA (LHH, BEM, NLP, MG); Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, Sweden (PH, PL, NLP, MG); Department of Psychology, Goteborg University, Goteborg, Sweden (BJ)
Correspondence to: Beth E. Meyerowitz, PhD, Department of Psychology, University of Southern California, Los Angeles, CA 90089-1061 (e-mail: meyerow{at}usc.edu).
Our recent article (1) reported that, in a population-based sample of twins, there was increased risk for cognitive dysfunction in long-term cancer survivors relative to their cancer-free co-twins. Cognitive dysfunction was found in 14.5% of cancer survivors and in 8.7% of twins who had not had cancer. Although clinically diagnosed dementia was twice as frequent among cancer survivors as in their co-twins, this difference was not statistically significant.
In an associated editorial, Wefel and Meyers (2) raised several concerns. In particular, they criticized use of telephone interviews to assess cognitive dysfunction. Although they did not state so explicitly, they seemed concerned both that the method was too insensitive to detect subtle cognitive sequelae (3) and that not everyone who scored poorly was sufficiently impaired to meet criteria for dementia.
In our assessment of cognitive function, errors that classified an individual as having cognitive dysfunction included inability to remember three common words for 90 seconds, to know the day of the week, or to explain how two familiar items were similar to each other. Classification as having cognitive dysfunction further required that an informant confirm that the individual's daily functioning (e.g., managing personal finances, living independently) was impaired due to problems of memory or cognition. The telephone assessment was not designed to identify subtle differences in cognitive functioning but to locate individuals whose cognition was obviously compromised. The fact that we found differences in rates of cognitive dysfunction between cancer survivors and their cancer-free co-twins indicates that the assessment was sensitive to important differences.
They also noted the "poor diagnostic accuracy" associated with the telephone interview. The telephone interview was never intended to be a measure of clinical dementia. Moreover, it is highly sensitive. Those who have dementia are detected (4). In any event, we do not think that concerns about cognitive sequelae in cancer survivors should be limited to frank dementia.
They urged consideration of the alternative hypothesis that cancer patients had poorer cognitive functioning before their cancer treatment. We agree with the value of longitudinal information. However, even if some cognitive problems existed prior to the cancer, it seems unlikely that the level of dysfunction observed in long-term survivors (14 years postdiagnosis on average) would have been present to any large extent before the cancer diagnosis.
Finally, they question whether recall error or interviewer bias might explain our findings. In our study, cancer diagnoses were taken from the national cancer registry, and cognitive screening was conducted independently from establishing cancer history and in a context where interviewers were blind to future use of the data to study late adverse health effects of cancer patients. Thus, we cannot see recall error or interviewer bias affecting the results.
The increasing number of cancer survivors makes studies of late adverse health effects important. Future individualized treatment regimens, built on better prognostic and therapy predictive markers, will most likely reduce the number of unnecessarily treated patients and thus late treatment-related sequelae. If future research confirms long-term or late effects on cognition following cancer treatment, patients and their health care providers deserve to have this information.
REFERENCES
(1) Heflin LH, Meyerowitz BE, Hall P, Lichtenstein P,Johansson B, Pedersen NL, et al. Cancer as a risk factor for long-term cognitive deficits and dementia. J Natl Cancer Inst 2005;97:8546.
(2) Wefel JS, Meyers CA. Cancer as a risk factor for dementia: a house built on shifting sand. J Natl Cancer Inst 2005;97:7889.
(3) Meyers CA, Wefel JS. The use of the Mini-Mental State Examination to assess cognitive functioning in cancer trials: no ifs, ands, buts, or sensitivity. J Clin Oncol 2003;21:35578.
(4) Gatz M, Reynolds CA, John R, Johansson B, Mortimer JA, Pedersen NL. Telephone screening to identify potential dementia cases in a population-based sample of older adults. Int Psychogeriatr 2002;14:27389.[CrossRef][ISI][Medline]
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