taVNS for Breast Cancer Pain and Symptom Management

• Active taVNS (Device): practice the active taVNS twice daily for 30 minutes each over a 4-week period (56 sessions)
• Sham taVNS (Device): practice the sham taVNS twice daily for 30 minutes each over a 4-week period (56 sessions)

Primary outcomes

• Feasibility of implementing taVNS - Retention rates [Baseline and 4 weeks and 8 weeks]: Feasibility will be assessed by evaluating the retention rate of participants who complete the taVNS sessions at 4 weeks and the follow-up at week 8. Retention rates will be calculated by comparing the number of participants who complete these timepoints with the baseline data.
• Adherence of implementing taVNS - Duration of usage [4 weeks]: Participants will log the frequency, time, and duration of daily taVNS device use in an online diary through the REDCap system.
• Incidence of Treatment-Emergent Adverse Events (Safety and Tolerability) [Baseline and 4 weeks and 8 weeks]: Incidence of Treatment-Emergent Adverse Events (Safety and Tolerability) in using the taVNS will be measured using self-reported data, including online self-monitoring diary, surveys, and interviews. Adverse events (AEs) will be monitored daily using the online diary with a preset form, including a 10-item survey to assess daily AEs of taVNS on 0-10 Likert scales.
• Satisfaction in implementing taVNS [Baseline and 4 weeks and 8 weeks]: Satisfaction in using the taVNS will be measured using self-reported data including online self-monitoring diary, surveys, and interviews.

Secondary outcomes

• Change in pain intensity and interference [Baseline and 4 weeks and 8 weeks]: Pain Inventory (BPI) will be used to assess the multidimensional aspects of pain, its location, intensity, and interference. A higher score indicated higher pain intensity with 0 indicating no pain and 10 indicating the worst pain. A higher score of pain interference means daily functions are more impacted by pain, and 0 indicates no pain interference, and 10 means the worst pain interference.
• Change in chronic pain self-efficacy [Baseline and 4 weeks and 8 weeks]: Chronic Pain Self-Efficacy Scale (CPSES) will be used to measure pain self-efficacy with scores from 0-100, higher scores indicating improved self-efficacy.
• Changes in quantitative sensory testing (QST) [Baseline and 4 weeks and 8 weeks]: Quantitative sensory testing (QST) will be used to measure sensitivity to experimental pain with standardized stimuli to test both nociceptive and non-nociceptive systems.
• Changes in conditioned pain modulation (CPM) [Baseline and 4 weeks and 8 weeks]: CPM will be used to determine the net effect of various facilitating and inhibiting systems exerting their activity at spinal or supraspinal levels. A phasic noxious stimulus (cold) will be applied in conjunction with a tonic noxious conditioning stimulus (pressure) applied to a distant body site on the forearm. Participants' self-reported pain intensity by NRS during the test will be recorded.
• Changes in symptoms: Physical Function [Baseline and 4 weeks and 8 weeks]: The Patient-Reported Outcomes Measurement Information System (PROMIS) profile will be used to measure the physical function. The T-score of PROMIS measurement ranges from 0 to 100 and a higher T-score indicates a more severe symptom reported by the subjects. A T-score greater than 50 means participants have more severe symptoms than the healthy population.
• Changes in symptoms: Anxiety [Baseline and 4 weeks and 8 weeks]: The Patient-Reported Outcomes Measurement Information System (PROMIS) profile will be used to measure the anxiety. The T-score of PROMIS measurement ranges from 0 to 100 and a higher T-score indicates a more severe symptom reported by the subjects. A T-score greater than 50 means participants have more severe symptoms than the healthy population.
• Changes in symptoms: Depression [Baseline and 4 weeks and 8 weeks]: The Patient-Reported Outcomes Measurement Information System (PROMIS) profile will be used to measure the co-occurring depression. The T-score of PROMIS measurement ranges from 0 to 100 and a higher T-score indicates a more severe symptom reported by the subjects. A T-score greater than 50 means participants have more severe symptoms than the healthy population.
• Changes in symptoms: Fatigue [Baseline and 4 weeks and 8 weeks]: The Patient-Reported Outcomes Measurement Information System (PROMIS) profile will be used to measure the co-occurring fatigue. The T-score of PROMIS measurement ranges from 0 to 100 and a higher T-score indicates a more severe symptom reported by the subjects. A T-score greater than 50 means participants have more severe symptoms than the healthy population.
• Changes in symptoms: Sleep Disturbance [Baseline and 4 weeks and 8 weeks]: The Patient-Reported Outcomes Measurement Information System (PROMIS) profile will be used to measure the co-occurring sleep disturbance. The T-score of PROMIS measurement ranges from 0 to 100 and a higher T-score indicates a more severe symptom reported by the subjects. A T-score greater than 50 means participants have more severe symptoms than the healthy population.
• Changes in symptoms: Ability to Participate in Social Roles and Activities [Baseline and 4 weeks and 8 weeks]: The Patient-Reported Outcomes Measurement Information System (PROMIS) profile will be used to measure the the ability to participate in social roles and activities. The T-score of PROMIS measurement ranges from 0 to 100 and a higher T-score indicates a more severe symptom reported by the subjects. A T-score greater than 50 means participants have more severe symptoms than the healthy population.
• Changes in pain-related cortical response [Baseline and 4 weeks and 8 weeks]: Cortical activity associated with pain stimuli will be assessed utilizing a continuous-wave, multichannel functional near-infrared spectroscopy (fNIRS) imaging system (LIGHTNIRS, Shimadzu, Kyoto, Japan) equipped with three semiconductor lasers emitting at 780, 805, and 830 nm. Optical data will be gathered while subjects undergo thermal pain stimulation.
• Measurement and comparison of fecal microbiota alpha diversity, beta diversity, and abundance of microbial taxa in the human gut [Baseline and 4 weeks and 8 weeks]: The 16S rRNA V4 region will be amplified and sequenced by using stool samples to depict the fecal microbiota alpha diversity, beta diversity, and abundance of microbial taxa in the human gut.

Sex: Female, ages: 18 Years to 79 Years

Inclusion Criteria:

1. are aged 18-79 years older;
2. have histologically confirmed Stage 0, I, II, or III breast cancer;
3. had completed their primary cancer treatment (surgery, radiotherapy, chemotherapy) and are currently on a stable survivorship care plan (e.g., endocrine therapy, supportive care), with no major treatment changes expected during the study;
4. have experienced pain with a severity of 4 or greater out of 10 for at least ten days in the last month;
5. are committed to maintaining the current treatment plan (e.g., endocrine therapy, supportive care) during the study;
6. have reliable internet access;
7. are willing to provide stool samples and undergo fNIRS brain imaging procedures;
8. are able to read and understand English and provide written informed consent.

Exclusion Criteria:

1. have metastatic breast cancer (Stage IV);
2. have a current diagnosis of another active cancer;
3. have a history of significant cardiac conditions, such as bradycardia, arrhythmia, recent myocardial infarction, or heart failure;
4. have been diagnosed with a severe psychiatric illness (e.g., schizophrenia, bipolar I disorder with active psychosis) that could interfere with adherence to study procedures;
5. have active inflammatory or malabsorptive gastrointestinal disorders (e.g., Crohn's disease, ulcerative colitis, celiac disease) that could confound gut microbiota results;
6. have taken antibiotics, probiotics, or gastrointestinal motility agents (e.g., laxatives, prokinetics) within the past 3 months, due to potential disruption of gut microbiota;
7. have a progressive neurological condition (e.g., Parkinson's disease, epilepsy, multiple sclerosis) that may impact fNIRS data quality or study participation;
8. have a history of surgical or pharmacological vagotomy or are currently receiving implanted vagus nerve stimulation therapy, because of potential interference with autonomic regulation and taVNS mechanisms;
9. have an active electronic or metallic implant (e.g., cochlear implant, pacemaker, neurostimulator) or other electronic/metallic device in the head or neck area, which may be contraindicated for taVNS;
10. are pregnant, breastfeeding, or planning to become pregnant during the study period;
11. have had a recent initiation or dose change of pain medications (e.g., opioids, neuropathic agents) within the past 4 weeks.