Canadian Breast Cancer Network

To enable the integration of novel therapies, it is critical to understand current long-term outcomes in HER2-positive metastatic breast cancer (mBC), including survival, treatment patterns, and costs. We sought to define these outcomes among patients with mBC in Ontario. We conducted a retrospective population-level study in Ontario women diagnosed with breast cancer of any stage between January 1, 2005 and December 31, 2019, with follow-up until December 31, 2020. HER2-positivity was based on receipt of a HER2-targeted therapy (HER2-TT) in the first line (1L) metastatic setting. Administrative databases at ICES were used to assess outcomes. In Ontario, 2557 patients were diagnosed with mBC and received a HER2-TT, and of these 1606 were diagnosed with early-stage (stage I-III) that became metastatic (recurrent), while 951 were diagnosed with late stage/de novo mBC (stage IV). The average age of all patients was 54.8years ± 12.7years. Treatment regimens that included pertuzumab and trastuzumab (cohort name: pert_tras) were the most frequently used HER2-TT for 1L mBC (51.4%), while T-DM1 was the most frequent therapy (87.5%) in second line (2L). The median overall survival (mOS) from initiation of 1L pert_tras was not reached, whereas mOS from initiation of T-DM1 in 2L was 18.7months. The overall mean cost per patient on pert_tras during 1L was $267,282. The main cost drivers were the cost of systemic therapy, followed by cancer clinic visits, with a mean cost per patient at $158,961 and $73,882, respectively. The baseline characteristics and treatment patterns for patients who received HER2-TT in our study align with previously reported results. However, the mOS observed for 2L T-DM1 was shorter than that found in pivotal, clinical trial literature. As expected, anti-cancer systemic therapy costs were the main contributor to the over quarter-million dollar mean cost per patient on pert_tras in 1L.

Trastuzumab is the standard treatment in Canada for patients with breast cancer positive for her2 (human epidermal growth factor receptor 2), dramatically improving outcomes in that patient group. However, its current intravenous (IV) administration is associated with long infusion times that place a significant burden on health care resources and patient quality of life. In an effort to provide a faster and easier administration method, a subcutaneous (sc) formulation of trastuzumab has been developed. Data from comparative trials demonstrate that the two formulations are comparable with respect to pharmacokinetics and efficacy. They also have similar safety profiles, with the exception of mild local and administration reactions with the sc formulation. Furthermore, the sc formulation is preferred by patients and health care professionals, and greatly reduces administration and chair time. Additional advantages include easier preparation and dosing, reduced drug wastage, and reduced discomfort at the injection site. By using well-thought-out administration procedures, the sc formulation can be given safely and effectively, potentially reducing the burden on health care resources and improving quality of life for patients.