Although protracted
cognitive impairment has been reported to occur after
radiotherapy even when such
therapy is not directed to brain areas, the mechanism remains unclear. This study investigated whether
breast cancer patients exposed to local
radiotherapy showed lower cognitive function mediated by higher plasma
interleukin (IL)-6 levels than those unexposed. We performed the Wechsler Memory Scale-Revised (WMS-R) and measured plasma
IL-6 levels for 105
breast cancer surgical patients within 1 year after the initial
therapy. The group differences in each of the indices of WMS-R were investigated between
cancer patients exposed to adjuvant regional
radiotherapy (n = 51) and those unexposed (n = 54) using analysis of covariance. We further investigated a mediation effect by plasma
IL-6 levels on the relationship between
radiotherapy and the indices of WMS-R using the bootstrapping method. The
radiotherapy group showed significantly lower Immediate Verbal Memory Index and Delayed Recall Index (P = 0.001, P = 0.008, respectively).
Radiotherapy exerted an indirect effect on the lower Delayed Recall Index of WMS-R through elevation of plasma
IL-6 levels (bootstrap 95% confidence interval = -2.6626 to -0.0402). This study showed that
breast cancer patients exposed to adjuvant regional
radiotherapy in conservation
therapy might have
cognitive impairment even several months after their treatment. The relationship between the
therapy and the
cognitive impairment could be partially mediated by elevation of plasma
IL-6 levels.