The investigators designed a prospective, 2-armed, cluster-randomized multicenter clinical trial on the effect of a by a digital application triggered intervention on quality of life and therapy-adherence among breast cancer patients, compared to standard of care.

With validated questionnaires, patient reported outcome monitoring data on quality of life, distress and therapy-adherence are collected. In case of pathologic values, the attending breast center gets advised to intervene according to individual requirements.

For women with breast cancer, disease and therapy come along with loss of quality of life. Therapy and its side effects often result in unauthorized discontinuation of therapy by patients. Non-adherence rates to endocrine therapy (ET) range from 31% to 73%. These patients have a poorer prognosis due to recurrence, progression and cancer deaths. Positive effects to increase therapy-adherence were shown for bidirectional communication. Furthermore the use of apps with reminder functions can increase adherence to cancer therapy. The intention within this project is to improve care of patients with primary breast cancer.

Inclusion Criteria:

• primary, hormone-sensitive breast cancer
• indication for adjuvant endocrine therapy (aromatase-inhibitor, tamoxifen, GnRH-analogue allone or in combination with tamoxifen/ aromatas inhibitor; combination of endocrine therapy with CDK 4/6-inhibitor/ antibody therapy/ radiotherapy)
• start of endocrine therapy <= 3 months ago
• patients with public health ensurance
• patients who are legally competent and able to understand and follow instructions of the study staff
• present informed consent

Exclusion Criteria:

• no use of internet or digital applications
• advanced, metastatic breast cancer
• simultaneous serious disease
• life expectancy < 2 years