Comparison of Mastectomy Expander Trial

Expanders are used outside their intended use, due to two following facts: It is possible that expander implantation exceed the "approved" duration of 6 months (maximal 10 months). Additionally, some participants will receive after mastectomy/expander implantation an adjuvant radiotherapy according to standard of care, which is either a contraindication of the medical device or not yet tested in-vivo by the manufacturer. Requested answers: * how good is the aesthetic outcome of the breast with the expanders and the final implants, and whether any complications occurred during treatment, * how satisfied are subjects and doctors with the outcome of the breast reconstruction, and how the reconstruction affects health-related quality of life from participants, * how does the structural composition of the removed expanders looks like, in order to understand whether radiation therapy has caused changes in the material, * which key immunological factors lead to increased hardening of the tissue around the expander, especially during radiation therapy (capsule formation).

Inclusion Criteria: * Understands and agrees to comply with the study procedures and provides informed consent as documented by signature * Female subjects aged ≥ 18 years at time of consent * INDICATION: Breast cancer diagnosis (malignancy) with neoadjuvant chemotherapy OR ductal carcinoma in situ (DCIS) diagnosis without neoadjuvant chemotherapy AND / OR positive genetic counseling for high-risk family history of breast cancer * RECONSTRUCTION MODALITIES: planned uni- or bilateral NSME or SSME with simultaneous prepectoral tissue expander-based breast reconstruction due to malignancy OR Planned prophylactic bilateral mastectomy with simultaneous prepectoral tissue expander-based breast reconstruction. Planned unilateral NSME or SSME and planned prophylactic contralateral mastectomy with simultaneous prepectoral tissue expander-based breast reconstruction * Ability to speak and read German to a level which allows fully comprehending the meaning of everything that is said or written. * Inclusion criterion 6 only applies to subject with radiotherapy: Adjuvant radiotherapy as part of the breast cancer treatment plan * Inclusion criterion 7 only applies to women of childbearing potential (WOCBP): negative urine pregnancy test, not breastfeeding Exclusion Criteria: * Subject with implanted device that may be affected by magnetic fields (pacemaker) * Known presence of HIV, viral hepatitis (patient-reported) * Presence of autoimmune disease(s) or immunocompromised subject due to immunosuppressive or steroid therapy * The subject is currently participating or intends to participate in another clinical trial that may interfere with the protocol of this study.