Wearable Enhanced Fitness Tracking for Metastatic Breast Cancer Patients Using Endocrine Treatment and Palbociclib

This study uses a fitness tracking watch and smartphone app to monitor physical activity in women with advanced (metastatic) breast cancer who are being treated with hormone-blocking therapy and a drug called palbociclib. Researchers want to understand how exercise habits change during treatment. **You may be eligible if...** - You are a woman aged 18 or older - You have been diagnosed with hormone receptor-positive, HER2-negative metastatic breast cancer - You have been on palbociclib combined with hormone therapy for at least 3 months - You own a compatible smartphone with internet access **You may NOT be eligible if...** - You have a serious uncontrolled medical condition (such as heart problems, active infection, or a serious psychiatric disorder) - Your life expectancy is less than 3 months - You have been on another experimental drug in the past 28 days - You have difficulty reading or using a smartphone app Talk to your doctor to see if this trial is right for you.