Inclusion Criteria:  Female patients aged ≥ 18 years with hormone-positive stage 0-3 breast cancer. Performance status ECOG 0-2. Ongoing daily adjuvant tamoxifen minimum of 2 months ± GnRH analogues ± RT for stage 3 breast cancer. Locally recurrent disease, previously treated with adjuvant tamoxifen. Able to use software applications developed specifically for small, wireless computing devices, such as smartphones and tablets. Have small, wireless computing devices, such as smartphones and tablets.  Exclusion Criteria:  Fulfilling any of the contraindications for tamoxifen. Metastatic (stage IV) breast cancer. Included in other clinical studies receiving not approved investigational medicinal drug. Ongoing pregnancy or lactation. Any psychological, familial, sociological, or geographical condition potentially hampering compliance with the study protocol and follow-up schedule.