Treatment patterns and associated outcomes among patients with HER2+ metastatic breast cancer in the United States: an observational cohort study.

Background: With treatment options for human epidermal growth factor receptor 2-positive (HER2+) metastatic breast cancer (mBC) expanding, updated assessments of contemporary treatment patterns and clinical outcomes are needed. This study aimed to conduct such an assessment using data from real-world oncology practices.

Materials and methods: Adult HER2+ mBC patients initiating first-line (1L) treatment from January 2013 to January 2021 (index date) were selected from the US Flatiron Health database and followed through January 2022. Patient characteristics and treatment patterns were summarized. Clinical outcomes were examined using Kaplan-Meier analyses.

Results: Among 2074 HER2+ mBC patients with at least 1 line of therapy (LoT), median age was 61 years and 62.8% had known hormone receptor-positive disease. During a median follow-up of 26.0 months, 1159 (55.8%) had at least 2 LoTs, and 584 (28.2%) had 3 or more. The most common 1L regimens included docetaxel, trastuzumab, and pertuzumab (THP; 38.9%) followed by THP+ platinum agent (7.5%) and ado-trastuzumab emtansine (T-DM1) monotherapy (6.1%). By the end of follow up, 18.1% of patients remained on treatment, 20.2% died, and 5.8% discontinued without starting a new treatment. Median overall survival from 1L start was 40.3 months.

Conclusions: Approximately one-quarter of the patients died or discontinued 1L therapy without receiving further treatment. Overall survival from the start of 1L was just over 3 years. This highlights a need for more effective therapies in earlier LoTs that prolong the time to progression and provide longer clinical benefits.