A named patient program (NPP) was initiated to allow patients with an unmet medical need to access trastuzumab deruxtecan (T-DXd) treatment. To gain early insights on the use of T-DXd outside of a trial setting, patients with advanced/metastatic HER2+ breast cancer receiving treatment (or previously treated) with T-DXd through the NPP will be invited to participate.

The antibody-drug conjugate T-DXd has been granted conditional approval in the European Union as a single agent for adult patients with unresectable or metastatic HER2+ breast cancer who have previously received ≥2 HER2-based regimens. This was based on data from the Phase II DESTINY-Breast01 trial (NCT03248492).

DS8201-0002-EAP-MA is a real world data (RWD) observational data collection inviting patients with advanced/metastatic HER2+ breast cancer receiving T-DXd through the NPP already to participate to help further understand the usage in a real world clinical setting.

Inclusion Criteria:

• Participants for whom T-DXd treatment is indicated, according to the summary of product characteristics conditionally approved by the EMA, that are eligible for treatment with T-DXd through the NPP (i.e., those with advanced/metastatic HER2+ breast cancer who have received ≥ 2 prior anti-HER2-based regimens and have documentation of HER2 positive tumour status by a validated method) will be eligible for inclusion to this RWD collection, subject to providing written informed consent to participate.

Exclusion Criteria:

• Any participant who does not meet all inclusion criteria noted above.

The real world data (RWD) collection will include adult participants with advanced/metastatic HER2+ breast cancer treated in routine clinical practice. The collection of RWD will be optional and independent to eligibility for the NPP. It will include those who have already completed T-DXd treatment under the NPP, as well as patients whose T-DXd treatment remains ongoing.