Digital Patient Support Program for Self-efficacy and Medication Adherence in Women on Adjuvant Endocrine Treatment for Breast Cancer

This study is testing whether a digital patient support app (called Sidekick) helps women with early-stage breast cancer stay on track with their hormone-blocking medications (adjuvant endocrine therapy) and feel more confident managing their health. **You may be eligible if...** - You are 18 or older - You have been diagnosed with stage I, II, or III breast cancer diagnosed on or after September 1, 2023 - You have been prescribed adjuvant endocrine therapy (hormone-blocking medication) - You understand written and spoken Icelandic or English - You own a compatible smartphone and are willing to use the Sidekick app **You may NOT be eligible if...** - You have other health conditions that your oncologist believes would interfere with the study - You are currently participating in another clinical study that could affect results Talk to your doctor to see if this trial is right for you.