Ncog-34. brain pet imaging of paired helical filament tau in older adults with cancer: pilot study to identify mechanisms of cognitive impairment after cancer therapy

Abstract BACKGROUND Cancer-related cognitive impairment (CRCI) occurs in up to 75% of patients treated with chemotherapy for systemic cancer, and older patients treated for CNS cancer receiving brain radiation therapy (RT) and chemotherapy are particularly at risk. The mechanisms of injury and CRCI remain unknown. In neurodegenerative disorders, deposition of paired helical filament tau (PHFTau) is correlated with nature and extent of cognitive symptoms. The role of PHFTau in CRCI has not been elucidated. We conducted a pilot study to determine whether CRCI is associated with PHFTau. METHODS Patients (age >60) diagnosed with mild cognitive impairment (MCI) or dementia after chemotherapy and/or brain RT underwent Tau PET imaging using [F18]Flourtaucipir. Cortical [F18]Flourtaucipir binding was quantified by standard uptake value ratio (SUVR) in 68 regions of interest (ROIs) and compared to a control group (n=22). SUVR in each ROI for each subject was considered significantly elevated when it was >2SD above the control group (p< 0.05). Neuropsychological test scores were correlated with PHFTau distribution. RESULTS Five patients with MCI/Dementia following cancer therapy participated. Two patients with prior chemo-RT for CNS cancer and prominent executive dysfunction had no significant F[18]T807 uptake. However, three patients treated with systemic chemotherapy for non-CNS cancer and neuropsychological profiles dominated by episodic memory impairment showed F[18]T807 uptake in patterns typical of AD dementia in temporal, parietal and cingulate ROI’s (n=2), or uptake in the entorhinal and inferior temporal ROIs (n=1). DISCUSSION In this pilot study, [F18]Flourtaucipir imaging of patients with cancer and MCI/Dementia showed that executive dysfunction after RT was not associated with abnormal PHFTau whereas amnestic declines after chemotherapy were associated with PHFTau in medial temporal lobes and beyond. Given the cross-sectional study, timing of tau accumulation in relation to cancer/treatment is unknown. Prospective studies are needed to understand the relevance of PHFTau in CRCI.