Real-World Treatment Patterns and Outcomes Following First-Line Pertuzumab and Trastuzumab Among Patients with HER2+ Metastatic Breast Cancer.

Introduction: Many patients with human epidermal growth factor receptor-2-positive metastatic breast cancer (HER2+ mBC) require subsequent lines of therapy (LOTs) after being treated with pertuzumab and trastuzumab-based regimens in the first line (1L). Although the efficacy of the second-line (2L) therapies has been demonstrated in clinical trials, the real-world effectiveness of these treatments is understudied. This retrospective cohort study assessed the real-world treatment patterns and outcomes for patients with HER2+ mBC following 1L therapy with pertuzumab and trastuzumab-based regimens in the United States (US) during 2015-2019.

Methods: Adults with HER2+ mBC in the US who initiated 1L pertuzumab and trastuzumab-based regimens between 01/01/2015 and 09/30/2019 and had ≥ 60 days of follow-up after 1L initiation were identified from the IQVIA Oncology Electronic Medical Records database. The regimens utilized in 2L following 1L pertuzumab and trastuzumab-based regimens were described. Median treatment duration and time to treatment failure were reported for 2L based on Kaplan-Meier analyses.

Results: Of the 710 eligible patients who received pertuzumab and trastuzumab-based regimens in 1L (median age: 57.0 years [interquartile range: 48.0-65.0]; median follow-up: 20.3 months; median 1L duration: 15.3 months), 222 (31.3%) initiated 2L. The most common regimens in 2L were ado-trastuzumab emtansine (T-DM1)-based regimens (n = 159 [71.6%]), followed by lapatinib-based (n = 21 [9.5%]) and neratinib-based (n = 18 [8.1%]) regimens. The median treatment duration and time to treatment failure were 5.9 (95% CI: 5.0, 8.7) and 8.6 (7.3, 11.5) months, respectively, among patients initiating 2L, and 5.7 (4.7, 7.8) and 7.9 (6.5, 10.0) months among those receiving 2L T-DM1.

Conclusions: Most patients with HER2+ mBC requiring additional treatments after 1L pertuzumab and trastuzumab-based regimens utilized T-DM1 in 2L during 2015-2019. The short median treatment duration and time to treatment failure highlight an unmet need that can potentially be fulfilled by recently approved treatment options.