In current clinical practice, breast cancer is treated according to hormone receptor and human epidermal growth receptor 2 expression (HER2) status, which play an important role in disease management and overall prognosis. Trastuzumab deruxtecan (T-DXd) has been studied in multiple global prospective DESTINY-breast trials. Recent marketing authorisation for T-DXd has been granted from Health Canada for HER2-positive breast cancer who have received prior treatment with trastuzumab emtansine, or at least one prior anti-HER2-based regimen in the metastatic setting, or who have received a prior anti-HER2-based regimen in the neoadjuvant or adjuvant setting and developed disease recurrence during or within 6 months of completing neoadjuvant or adjuvant therapy. T-DXd is also indicated for HER2-low unresectable and/or metastatic breast cancer (mBC) patients 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. However, there is a paucity of evidence assessing T-DXd in the real-world setting. As such, the overarching aim of this study is to generate Canadian real-world evidence on discontinuations and treatment modifications for patients with HER2+ and HER2-low mBC undergoing treatment with T-DXd.

This is a hybrid, longitudinal cohort study design leveraging patient support programme (PSP) secondary data with additional primary data collection to assess study treatment-related outcomes among patients with HER2+ and HER2-low mBC receiving treatment with T-DXd. Mainly, this study will leverage secondary data from the PSP, which will include clinical and demographic characteristics as well as duration, modification and intensity of treatment information for patients while enrolled in the PSP. These data will be supplemented with primary data, which will be collected via a patient questionnaire and include additional self-reported clinical and demographic characteristics not captured within the PSP, including follow-up data on therapies received, treatment discontinuation information after the PSP closure and frequency of CT scans and cardiac monitoring scans.

The study protocol was approved by the Advarra Institutional Review Board on 13 December 2023 (ID: D133HR00037). Findings will be disseminated by publication in peer-reviewed journals, through oral and poster presentations for various audiences, websites and scientific meetings. Written informed consent will be obtained from all patients prior to agreeing to participate in this study.

Participant recruitment for primary data collection began on 22 April 2024 and was completed on 8 October 2024. Primary data collection for follow-up will continue through up to 12 months after the date of the last enrolment.

NCT06386263.