Collection of data in real life conditions on satefy, effectiveness and quality of life of trastuzumab deruxtecan in patients with metastatic or unresectable HER2-positive breast cancer.

The present observational study aims to collect data on long-term safety of trastuzumab deruxtecan, with a primary endpoint on trastuzumab deruxtecan related adverse drug reactions (ADRs) of interest. Data on patient profile, treatment history (before, during and after trastuzumab deruxtecan administration), effectiveness and health-related quality of life will also be collected in a real-life setting, to confirm and complement data from clinical trials. Patients will be recruited whether they have started trastuzumab deruxtecan treatment or will start it at the time of inclusion, whether they were prescribed compassionate trastuzumab deruxtecan or marketed Enhertu®, in order to rapidly collect a large set of data.

Inclusion Criteria:

• Male or female adult patient (age ≥ 18 years);

• Unresectable or metastatic HER2+ breast cancer, previously treated with at least 2 lines of anti-HER2, and:

  • previously treated by compassionate trastuzumab deruxtecan (ATU group), or
  • previously treated or planned to be treated by trastuzumab deruxtecan (Enhertu®), upon the investigator's decision (Post-Marketing authorization group);

• Patient who expresses non-opposition to participate in the study, or deceased patient who did not express his/her opposition to the use of his/her personal data while alive.

Exclusion Criteria:

- Previous participation in an interventional clinical trial with trastuzumab deruxtecan

Unresectable or metastatic HER2+ breast cancer, treated at least once with trastuzumab deruxtecan