TAO-Towards Optimal (Neo)Adjuvant Systemic Therapy of Stage III Triple-negative Breast Cancer

Inclusion Criteria: * Patients aged 18 years or older * Histologically confirmed adenocarcinoma of the breast * Assumed clinical or pathological stage III (TNM) breast cancer * Breast tumor must be: * HER2-negative: i.e. either score 0 or 1 at immunohistochemistry or score 2 at immunohistochemistry and negative at in situ hybridization (ISH, CISH or FISH) * Hormone receptor negative i.e. an estrogen receptor (ER) of \<10% and progesterone receptor (PR) of \<10%.; or in case of a histological grade III tumor an ER of \<50% and a PR of \<50%. * Patients are planned to receive the complete standard of care in the Netherlands; neo-adjuvant chemotherapy according to local practise * Participating patients have to be able to use a mobile phone, tablet, laptop and/or computer and understand the Dutch language Exclusion Criteria: * Evidence of distant metastases. Staging examinations should have been performed according to Dutch national guidelines. * Patients who are only treated systemically in the adjuvant setting * Participation in another clinical study with an treatment intervention during the course of this study.