Feasibility, Usability, Adherence, and Health Outcomes of Coaching App with Limb Swelling Monitoring for Self-Management in Patients with Breast Cancer-Related Lymphedema: 12-Week Results of a Single-Arm Longitudinal Study (Preprint)

BACKGROUND Breast cancer-related lymphedema (BCRL) is a chronic condition requiring lifelong self-management. Patients often face barriers such as limited physical function, time constraints, low self-efficacy, and inconsistent information. Objective limb swelling assessment is critical for effective self-management; however, most patients lack reliable home-monitoring tools that integrate measurements with evidence-based feedback to drive behavioral change. OBJECTIVE We evaluated the feasibility, usability, and preliminary clinical efficacy of an integrated digital health intervention—a mobile app with evidence-based coaching features and a smart tape measure—designed to support objective self-monitoring and behavioral changes in patients with BCRL. METHODS A 3-month multicenter single-arm prospective study enrolled 58 female patients with BCRL. Participants used the "Second Doctor" app and smart tape measure for weekly arm volume monitoring. The application provides real-time visualization of the percentage of excess volume, self-management feedback, and coaching recommendations derived from clinical guidelines. Measurement validity was determined by correlating the self-measured volumes with Perometer (optoelectronic perometry) measurements. Feasibility was assessed based on retention and adherence rates. Usability was evaluated using a System Usability Scale (SUS) and a technology-acceptance model-based questionnaire. Clinical outcomes included limb volume changes, quality of life (LYMQOL), International Classification of Functioning, Disability, and Health (ICF) domains, and Transtheoretical Model (TTM) stages of self-management behavior. RESULTS The smart tape measurement demonstrated a strong correlation with the Perometer measurements (forearm r = 0.662, P < 0.001; whole arm r = 0.767, P < 0.001), validating its accuracy for home monitoring. Fifty-two participants completed the study (89.6% retention), with high adherence averaging 5.0 measurements monthly. Usability was good (SUS mean: 68.94, SD: 12.08), with high satisfaction scores (mean ≥ 4.0 on a 1–6 scale) across usefulness, ease of use, attitude, motivation, and recommendation willingness. Participants reported significant advancement in TTM stages (mean difference = −0.35, P = 0.02) and improvements in LYMQOL appearance (P = 0.04) and overall QoL (P = 0.03), alongside ICF improvements in body image (P = 0.03), physical endurance (P = 0.01), and muscle power (P = 0.02). The overall limb volume remained stable; however, subgroup analysis revealed that participants advancing in TTM stages (n = 13, 25%) maintained a stable volume, whereas those without behavioral progression (n = 39, 75%) showed significant increases (P = 0.03), demonstrating a direct link between behavioral engagement and clinical outcomes. CONCLUSIONS An evidence-based coaching application integrated with validated self-monitoring is feasible, acceptable, and clinically meaningful for the self-management of BCRL. The intervention achieved consistent engagement, positive usability, and behavioral improvements, translating to volume stability among the engaged patients. This system enables patient-driven disease management and offers a scalable solution for lymphedema care by closing the loop between objective measurements, real-time feedback, and evidence-based guidance. CLINICALTRIAL This trial was registered at ClinicalTrials.gov (identifier: NCT06922513; initial release: March 19, 2025)