Trajectories of cognitive function prior to cancer diagnosis: a population-based study

BACKGROUND: An emerging body of research suggests that non-central nervous system (CNS) cancer may negatively impact the brain apart from effects of cancer treatment. However, studies assessing cognitive function in newly diagnosed cancer patients cannot exclude selection bias and psychological effects of cancer diagnosis. To overcome these limitations, we investigated trajectories of cognitive function of patients before cancer diagnosis. METHODS: Between 1989 and 2013, 2059 participants from the population-based Rotterdam Study were diagnosed with non-CNS cancer. Cognitive assessments were performed every three-five years using a neuropsychological battery. The general cognitive factor was composed of individual cognitive tests to assess global cognition. Using linear mixed models we compared change in cognitive function of cancer cases before diagnosis with cognitive change of age-matched cancer-free controls (1:2). In addition we performed sensitivity analyses by discarding assessments of controls five years before the end of follow-up to exclude effects from potential undiagnosed cancer. All statistical tests were two-sided. RESULTS: The Word Learning Test immediate recall declined faster among cases than among controls (-0.05 [95%CI=-0.09;-0.01] versus 0.01 [95%CI=-0.01;0.03], P for difference=.003). However, this difference was not statistically significant in sensitivity analyses. Furthermore, no statistically significant differences were observed in change of other individual cognitive tests and of the general cognitive factor. CONCLUSION: In this study we evaluated cognitive function in a large group of cancer patients prior to diagnosis, thereby excluding the psychological impact of cancer diagnosis and biased patient selection. In contrast to previous studies shortly after cancer diagnosis, we found no difference in change of cognitive function between cancer patients and controls.