This retrospective observational study will collect Canadian real-world data (RWD) from HER2+ metastatic breast cancer (mBC) patients to describe treatment sequences of all therapies received in the metastatic setting, to measure overall survival (OS), progression free survival (PFS), time to next active anti-cancer therapy, and to estimate the health resources utilization (HRU) during third-line therapy.

The proportion of treatment received during all lines of therapy in the metastatic setting will be described. The 2-year survival rate and median OS with interquartile range (IQR) for third-line therapy will be calculated. HRU data and costs during third-line therapy will be collected.

Inclusion Criteria:

Male or female patients (≥18 years of age)

Patients with stage IV breast cancer

Patients with HER2+ status in metastatic setting

Patients that received at least two lines of active anti-cancer drugs due to disease progression.

Patients that began third-line therapy prior to October 31, 2018.

Exclusion Criteria:

Patients treated with an investigational anticancer agent in the ≥ 3rd line setting

The study population in this study will include up to 100 patients with HER2+ mBC having completed at least two previous lines of anti-HER2 based therapy or a combination of anti-HER2 based therapy and chemotherapy and ongoing third or additional lines of treatment.

The results of this retrospective observational study will not be formally documented in a Clinical Study Report. Coded patient-level data will be shared with the sponsor.