The inclusion of trastuzumab-based therapy with chemotherapy was associated with improved survival outcomes compared with chemotherapy alone for the third-line treatment of metastatic breast cancer, according to a study presented at the 2021 San Antonio Breast Cancer Symposium.

The Flatiron Health database was used to identify patients with metastatic breast cancer previously treated with anti-HER2 therapies and who initiated third-line treatment with chemotherapy plus trastuzumab-based therapy or chemotherapy alone between January 2012 and December 2020.

Direct average treatment effects of initiating trastuzumab-based therapy plus chemotherapy vs chemotherapy were estimated using an intention-to-treat approach on the hazard ratios (HRs) for overall survival (OS) and real-world progression free survival (rwPFS). Average treatment effect was estimated using inverse probability of treatment weighting for Cox-proportional hazard models.

A total of 337 patients were included in the study, of these 288 initiated trastuzumab-based therapy plus chemotherapy and 49 received chemotherapy alone. Median OS was 23 months for trastuzumab-based therapy plus chemotherapy and 11 months for chemotherapy alone. Median rwPFS were 6 months and 5 months, respectively.

In the weighted population, median OS was 19 months for trastuzumab-based therapy plus chemotherapy and 10 months for chemotherapy alone (HR = .29 [.15-.54]). Median rwPFS were 6 months and 5 months, respectively (HR = .69 [.45-1.06]).

“Including trastuzumab-based therapy in addition to CT [chemotherapy] in the third-line treatment was associated with markedly improved survival outcomes compared with CT only,” concluded study authors.

Sanglier T, Ross R, Shi T, et al. Comparative effectiveness of initiating chemotherapy with or without trastuzumab based regimens as third line treatment for metastatic breast cancer. Presented at: 2021 San Antonio Breast Cancer Symposium; December 7-10, 2021; virtual. Abstract P2-13-22.