Trastuzumab deruxtecan (T-DXd) has been studied in multiple global prospective DESTINY-Breast trials and has a marketing authorization from Health Canada for patients with HER2-positive metastatic breast cancer (mBC) and HER2-low mBC, respectively.

Multiple stakeholders, including clinicians, patients, regulators, and healthcare decision makers, are interested in real-world treatment-related outcomes in order to better represent the effectiveness of therapies in routine care settings.

This is a non-interventional, observational, hybrid (involving both primary and secondary data), cohort study that is utilizing patient support program (PSP) data. PSPs in Canada can support patients in accessing medicines after Health Canada has granted marketing authorization of a new drug or new indication before public reimbursement is available.

The outcomes will be assessed for the HER2-positive and HER2-low cohorts separately.

The primary objectives include assessing early treatment discontinuation rates at 3-, 6-, and 9-months after initiating T-DXd, and characterizing T-DXd dose modifications (i.e., interruptions and reductions) over the course of treatment for HER2+ mBC and HER2-low mBC.

Secondary objectives include estimating the real-world time to discontinuation (rwTTD) of T-DXd, reasons for treatment discontinuations, and real world duration of treatment and dose intensity with T-DXd.

The primary analysis population for all primary and secondary objectives will be the Total PSP Population (TPP), which includes all patients enrolled into the PSP who meet study criteria. Sensitivity analyses will also be performed in the Study PSP population (SPP), which will be a subset of patients from the TPP who provide study consent for additional data collection.

Inclusion Criteria:

Enrollment criteria for HER2-positive PSP:

• Adults, 18 years of age or older
• Unresectable or metastatic HER2-positive breast cancer who have received at least one prior anti-HER2-based regimen either in the metastatic setting, or in the neoadjuvant or adjuvant setting and developed disease recurrence during or within 6 months of completing neoadjuvant or adjuvant therapy
• Patients must not have received a prior anti-HER2 ADC, such as trastuzumab emtansine, in the metastatic setting
• Patients who received a prior anti-HER2 ADC in the adjuvant setting must have progressed >12 months following the completion of therapy

Enrollment criteria for HER2-low PSP:

• Adults, 18 years of age or older
• Unresectable or metastatic HER2-low (IHC 1+ or IHC 2+/ISH-) breast cancer who have received at least one prior line of chemotherapy in the metastatic setting or developed disease recurrence during or within 6 months of completing adjuvant chemotherapy
• Patients with HR+ breast cancer should have received at least one or be considered ineligible for endocrine therapy.

Patients in the SPP must additionally meet the following criteria:

• Patients must have provided consent to be contacted for future research and provided consent to participate in the current observational study

Exclusion Criteria (both cohorts):

• Patients who enrolled in the PSP, but did not initiate therapy with T-DXd by the end of the PSP program
• Patients with medical history of Interstitial Lung Disease (ILD) / pneumonitis that required steroids or current ILD /pneumonitis
• Patients who do not have adequate renal or hepatic function, defined as:
• Inadequate renal function is defined as Creatinine clearance <30 mL/min, as calculated using the Cockcroft-Gault equation .
• Inadequate hepatic function is aspartate aminotransferase (AST)/alanine aminotransferase (ALT) >5 × upper limit of normal (ULN). Total bilirubin >1.5 × ULN if no liver metastases or ≥ 3 x ULN in the presence of documented Gilbert's syndrome (unconjugated hyperbilirubinemia) or liver metastases at baseline.

Patients with unresectable or metastatic HER2-positive or HER2-low breast cancer enrolled in the PSP who started treatment with T-DXd.

Qualified researchers can request access to anonymized individual patient-level data from AstraZeneca group of companies sponsored clinical trials via the request portal Vivli.org. All requests will be evaluated as per the AZ disclosure commitment: https://astrazenecagrouptrials.pharmacm.com/ST/Submission/Disclosure.

"Yes", indicates that AZ are accepting requests for IPD, but this does not mean all requests will be approved.

AstraZeneca will meet or exceed data availability as per the commitments made to the EFPIA/PhRMA Data-Sharing Principles. For details of our timelines, please refer to our disclosure commitment at https://astrazenecagrouptrials.pharmacm.com/ST/Submission/Disclosure

When a request has been approved AstraZeneca will provide access to the anonymized individual patient-level data via secure research environment Vivli.org. A Signed Data Usage Agreement (non-negotiable contract for data accessors) must be in place before accessing requested information.