Oncological therapies often go with the occurrence of partly serious undesirable side effects. Due to the therapy protocols, the patients are only in the oncological practice at certain time intervals. In order to be able to react adequately to side effects associated with therapy, these must be recognized early and monitored during the course. Due to the time intervals between visits to the doctor, patients have often forgotten important information about side effects, intolerance, as well as general well-being, or consider this information to be irrelevant or therapy-related. In order to obtain this information easily and then use it without extensive documentation by the patient, we have developed an app called NEMO for side effect management in oncology.NEMO is intended to enable patients to log important information on side effects of the therapy in a simple and standardized manner and to be able to log them over the entire course of therapy. There is a special focus on data security. The data is not transmitted online but only at the patients request via QR code during the doctors appointment.This is what the app does:* Clear presentation and operation, with the aim of enabling the application to be used by as many age groups as possible.* Optional acoustic accompaniment to assist in querying the side effects.* The answers of the app according to the common tumor therapy side effect evaluation system (CTCAE) enable an easy interpretation for the doctor.* Additional side effects of targeted tumor therapy are supported.* Entries are only saved locally on the smartphone and the data is only transmitted directly to the doctor using QR codes. There is no data transfer over the Internet.