Long-term influence of adjuvant breast radiotherapy on cognitive function in breast cancer patients treated with conservation therapy

Background The mechanisms underlying cognitive decline after radiotherapy not directed at brain areas remains unclear. We previously suggested that adjuvant breast radiotherapy in breast conservation therapy could lower memory function soon after therapy, and that the process might be partially mediated by plasma interleukin (IL)-6 levels. The present study investigated how that relationship changes longitudinally. Methods We performed the Wechsler Memory Scale-Revised (WMS-R) test and measured plasma IL-6 levels for 47 breast cancer surgical patients within 1 year after the initial therapy (study 1) and more than 2 years after study 1 (study 2). We also performed 2 × 2 mixed [the radiotherapy group ( n = 25) or the no-radiotherapy group ( n = 22) × study 1 or study 2] analysis of covariance on the WMS-R indices and plasma IL-6 levels. The association between changes in plasma IL-6 levels and changes in the WMS-R indices between the two studies was evaluated using Pearson’s correlation coefficient. Results The Immediate Verbal Memory Index was significantly higher in study 2. The Delayed Recall Index was significantly higher in study 2 and significantly lower in the radiotherapy group only in study 1. There was a significant correlation between changes in plasma IL-6 levels and changes only in the Delayed Recall Index of the WMS-R. Conclusions Memory decline in breast cancer patients soon after adjuvant breast radiotherapy was restored approximately 3 years after treatment, and decreased plasma IL-6 levels might be involved in the recovery process.