Transcranial Direct Current Stimulation for Cancer-related Cognitive Impairment in Breast Cancer Survivors

FACT-Cog is a validated self-report instrument designed to assess perceived cognitive function in cancer patients and survivors. It evaluates the individual's subjective experience of cognitive abilities during and after cancer treatment. Higher total scores reflect better perceived cognitive functioning. Only the overall score will be used as the outcome measure in this study.

Executive function will be assessed using the Trail Making Test, including Part A (visual attention and processing speed) and Part B (task switching and cognitive flexibility). Higher completion times reflect poorer performance. The difference in completion time from baseline will be used as the outcome.

Working memory will be assessed using the Digit Span Test (forward and backward conditions). Scores reflect the maximum number of digits recalled in correct order.

Verbal memory will be assessed using the Auditory Verbal Learning Test (AVLT), including immediate recall (sum of trials), delayed recall, and recognition accuracy. Scores reflect the number of correctly recalled or recognized items.

The Piper Cancer-Related Fatigue Scale (PFS) is a validated self-report instrument used to assess the severity of cancer-related fatigue. It contains 22 items scored on a 0-10 scale, with higher total scores indicating greater fatigue severity. Only the total score will be used as the outcome measure.

The changes in HAMD will constitute the secondary research outcome. The Hamilton Depression Scale (HAMD), compiled by Hamilton in 1960, is the most common clinical scale to assess depression. In this study, 17 versions were selected, and there were 17 questions. Each question scored between 0 and 4 points. Higher scores indicate more depressive symptoms. The severity of the disease and the therapeutic effect can be evaluated after treatment.

Endpoint: Difference between each time point's total score and baseline; negative Δ indicates symptom relief.

Analysis: Repeated measures mixed-effects model, exploring the moderating effect of mood on cognitive outcomes.

The Hamilton Anxiety Scale (HAMA) was compiled by Hamilton in 1959. It was one of the most commonly used scales in psychiatric clinics, including 14 items. It is often used in clinical diagnosis and degree classification of anxiety disorder.

Endpoint: Difference between each time point's total score and baseline; negative Δ indicates symptom relief.

Analysis: Repeated measures mixed-effects model, exploring the moderating effect of mood on cognitive outcomes.

The change of resting-state functional connectivity strength between the stimulated target and the whole brain areas will be measured by functional magnetic resonance imaging (fMRI): within-subject changes in (1) resting-state functional connectivity among key networks, (2) regional brain volumes (e.g., prefrontal cortex, hippocampus), and (3) white matter integrity (fractional anisotropy, mean diffusivity), reflecting tDCS effects on brain structure and function.

The change of resting-state functional connectivity strength between the stimulated target and the whole brain areas will be measured by resting-state electroencephalography (EEG): preprocessing (filtering, artifact removal), computation of relative power in δ/θ/α/β/γ bands, and extraction of P300 amplitude and latency. Endpoint: Difference in spectral power and ERP metrics relative to baseline. Analysis: Repeated measures ANOVA with post-hoc Bonferroni correction.