The study was discontinued due to low recruitment rates. Despite various measures, such as training courses and workshops, recruitment rates could not be improved in the long term.

Multicenter, prospective, randomised and controlled study to evaluate the medidux™ app during an observation period of 12 weeks (maximum 16 weeks in case of shifts in the initially planned therapy).

The PRO2 study is being conducted by palleos healthcare GmbH, the sponsor of the study, with the participation of an expected 585 patients at 40 study sites in Germany and 10 study sites in the German-speaking part of Switzerland with the aim of investigating the medical benefit of the smartphone application medidux™ (app) with regard to the occurrence of side effects in breast cancer therapy. Furthermore, the potential impact on the application of the chemotherapy or antibody-drug conjugate, respectively, the number of unplanned doctor visits, as well as hospitalizations and how often the app is used will be investigated.

The app was developed by mobile Health AG and is intended to accompany therapy. It is an approved CE-marked medical device that will be used in the study within the intended purpose. Study participants can use the app to document symptoms and well-being, as well as vital signs (e.g., blood pressure), and complete a test that can be used to assess mental performance. The entries can be viewed by the study physician through the medidux™ web application. The study participants can refer to the entries during the treatment visit to explain the course of therapy and perceived symptoms. As part of the study, use of the app will be compared to the normal treatment routine (without the app). A randomization process will determine whether study participants receive the app. The probability of receiving the app is 50%. If study participants receive the app, it can be used after installation on the personal smartphone. The approximately 12- to a maximum of 16-week observation period begins with the regular breast cancer therapy. The specific treatment of the breast cancer is not interfered with during the study, i.e. the administration of the therapy itself is carried out in the same way as it would be without the app.

Inclusion Criteria:

1. Patients with signed informed consent.

2. Female and male patients, age at diagnosis 18 years and older.

3. Patients with HER2-positive breast carcinoma* (confirmed by a local pathologist).

4. Patients with breast carcinoma with positive or negative hormone receptor status.

5. Patients prior to initiation of neoadjuvant, adjuvant or palliative chemotherapy** in combination with HER2-targeted therapy (including tyrosine kinase inhibitors [TKI]) or an antibody-drug conjugate therapy.

6. ECOG performance Status ≤ 1.

7. Sufficient command of the German language as assessed by the investigator.

8. Presence of a personal smartphone with iOS or Android system. The operating system must be updated to the latest, second or third most recent major version and the medidux™ app must be installed prior to the start of the first treatment cycle.

   • * HER2-positive in the context of the study defined as "eligible for an approved HER2-targeted therapy," i.e., in addition to immunohistochemistry (IHC) scores of 3+ and 2+ with positive results of in-situ hybridization (ISH+), also according to new standard HER2 low (IHC 1+ and 2+ with simultaneous negative result of in-situ-hybridization (ISH-))
   • ** Patients receiving chemotherapy in combination with HER2-targeted therapy as part of a (neo)adjuvant sequence therapy (e.g. as second part after previous EC therapy) may be included. Accordingly, the PRO2 study will not start until patients begin combination of chemotherapy and HER2-targeted therapy.

Exclusion Criteria:

1. Patients for whom it is questionable whether they will follow the study protocol, e.g., due to psychological problems or their private life situation.
2. Patients with insufficient knowledge about the use of smartphones.
3. Patients at the start of therapy with an ECOG performance status ≥ 2.
4. Patients who have already used the medidux™ app or its predecessor consilium care™ before admission to the study.
5. Patients with breast carcinoma who are to be treated exclusively with HER2-targeted antibody monotherapy or TKI-therapy without simultaneous chemotherapy. The sole administration of antibody-drug conjugates alone is permitted/prescribed by the SmPC.
6. Simultaneous participation in an interventional clinical trial.