With an incidence of approximately 69,000 cases per year in Germany, breast cancer is the most common cancer of women. About one in eight women is currently suffering from breast cancer, three out of ten affected are younger than 55 years. Breast cancer patients have to cope with a variety of symptoms, side effects and secondary effects. These include u. a. Fatigue, weight gain, decrease in muscle strength and bone density, pain, anxiety and depression, reduced participation in social and professional life and reduced quality of life. The most effective strategy to address these problems after oncological disease is physical activity. Physical activity enhances well-being, quality of life and survival after cancer. Physical activity also contributes to increasing the ability to work. This is particularly important for cancer patients, as returning to work is understood by most to be a return to normal and has a positive effect on self-esteem, mental health and quality of life. However, the absorption of physical activity is difficult precisely because of the above-mentioned symptoms. The medical rehabilitation can provide assistance and lay the foundation for the absorption of physical activity. In order to transfer the absorbed physical activity from the rehabilitation into the everyday life, adequate aftercare strategies are needed. Due to the legal situation, it is currently not possible to provide follow-up care after rehabilitation for oncological patients. The use of alternative offers such as rehabilitation sports or functional training often fails due to structural or local conditions.

Mobile health (also called "mHealth") offerings, ie offers that electronically support healthcare with the help of mobile devices, are increasingly becoming the focus of (research) interest. The aftercare app for breast cancer patients is based on the evaluated "New Credo" aftercare concept and supports breast cancer patients in continuing their physical activities learned during rehabilitation in their daily lives. An increase in social and professional participation, a more frequent and faster return to work and an increase in the quality of life are expected. In addition, we expect a reduction in physical, psychological and occupational burdens as well as a more favorable forecast of gainful employment and a better ability to work.