The MINIMAX study is a multicenter observational registry study in cN+ breast cancer patients treated with NST (chemotherapy and immunotherapy) in order to gain insight in oncologic safety and impact on QoL of less and more invasive axillary staging and treatment strategies.

Patients who are included in this study will complete Patient Reported Outcome Measures (PROMs) at baseline (time of diagnosis) and 1 and 5 years after diagnosis to assess impact on QoL. A database will be built by the Netherlands Cancer Registry. Data on patient-, tumor-, pre-NST staging-, post-NST staging- and treatment-characteristics are retrieved from patients' records by trained data registrars of the Netherlands Comprehensive Cancer Organisation (IKNL) using electronic case report forms (eCRFs). Five-year survival and recurrence will be evaluated to determine oncologic safety.

The results will be incorporated in the national guidelines. In case of an equilibrium between less and more invasive strategies, the data of this study will at least be extremely suitable to be used in the shared decision making process.