Abstract Background: Endocrine therapy (ET) is an integral treatment for early-stage hormone receptor-positive (HR+) breast cancer, but significant side effect burden can lead to decreased adherence and increased risk of recurrence. Chronotherapy, or aligning medication timing with circadian rhythms, has shown promise in reducing toxicity and improving efficacy of medications in other malignancies, but remains underexplored in breast cancer and ET. We conducted a pilot study to evaluate the feasibility of monitoring circadian rhythms in patients receiving ET using wearable digital health sensors and validated patient-reported outcomes (PROs). Methods: Patients with early-stage HR+ breast cancer already receiving or planning to initiate standard ET were eligible to enroll in a 14-day pilot study. Primary endpoint was to establish the feasibility of novel telemonitoring techniques to identify personalized circadian rhythms. Patients wore digital health devices including a wristwatch and a chest sensor to capture continuous physiologic data, including rest-activity, sleep-wake cycles, skin temperature, and heart rate continuously for 24 hours a day. Baseline symptom surveys were administered using the Pittsburgh Sleep Quality Index (PSQI) and Munich Chronotype Questionnaire (MCTQ). Patients completed daily PROs using the Karolinska Sleepiness Scale (KSS) and Functional Assessment of Cancer Therapy-Endocrine Subscale (FACT-ES) to capture ET-related symptoms and sleep-wake patterns. Results: As of 7/9/25, 11 of 20 patients (pts) have completed the study. Average pt age is 59.2 years (range: 32-86 years). 2/11 of pts self-identified as Black and 9/11 as White; 2 were premenopausal. All pts were on endocrine monotherapy: 5 anastrozole, 2 tamoxifen, 2 letrozole, and 2 exemestane. On average, pts had taken their ET for 9.5 months (range 0 - 43) prior to study entry. Five patients took their ET “early” (between 05:00 - 13:00) and 6 took their ET “late” (between 20:00 - 22:00). Pts completed greater than 96% of all surveys. The average FACT-ES score was 70.9 in the “early” group versus 63.1 in the “late” group (p.05). The average KSS was 2.7 in the “early” group versus 5.6 in the “late” group (p.05). At the end of the study, 10 of 11 pts (91%) reported it was “very easy” or “easy” to participate in the study while continuing daily life. Thus far, descriptive data of rest-activity, sleep-wake, and temperature rhythms highlight the individual variability in circadian rhythms between patients. Analyses to derive the circadian metrics are ongoing. Conclusions: Telemonitoring of circadian rhythms using wearable sensors is feasible and well-tolerated in patients receiving ET for HR+ breast cancer. Preliminary data suggest excellent patient adherence and feasibility of such telemonitoring approach, as well as increased ET-related symptoms and sleepiness in the “late” as compared to “early” ET groups. Further analysis will explore circadian rhythm metrics and associations with ET-related symptom burden. These findings support the feasibility of designing future research aimed at personalizing ET timing based on individual circadian profiles to improve tolerability and adherence. Citation Format: S. Poland, N. Chen, X. Li, B. Tucker, F. Lévi, E. Tasali, R. Nanda. Feasibility of Telemonitoring of Personalized Circadian Rhythms in Patients with Early-Stage HR-Positive Breast Cancer Receiving Endocrine Therapy abstract. In: Proceedings of the San Antonio Breast Cancer Symposium 2025; 2025 Dec 9-12; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2026;32(4 Suppl):Abstract nr PS3-10-11.
Poland et al. (Tue,) studied this question.