Trastuzumab based regimen was the most common anti-HER2 drug regimen during study timeframe. Despite availability of multiple anti-HER2 drugs, reuse of prior anti-HER2 drugs and switching to non-targeted therapies alone were common after using two anti-HER2 regimens. Recently approved anti-HER2 agents may provide additional treatment options for patients with pre-treated HER2-positive (+) metastatic breast cancer (mBC).

A retrospective study was conducted using patients with mBC diagnosis, HER2+ status documented in Surveillance, Epidemiology, and End Results or claims of one or more anti-HER2 drug, continuous enrollment in Medicare from the date of mBC diagnosis until end of study period/death, and two anti-HER2 regimens with or without chemotherapy (Ch) or hormonal therapy (HT) were included. The first two anti-HER2 regimens and subsequent therapies were summarized. Trastuzumab (T) based regimen was the most common first regimen, followed by T plus pertuzumab (+P), and lapatinib (L). For the second regimen, T was most common, followed by T+P, L, trastuzumab emtansine (T-DM1), and T+L was the least common. After a second regimen, 72% initiated a subsequent therapy, with over half switching to non-targeted therapies followed by T, T-DM1, and T+P. Among those with subsequent therapy, two T-based regimens followed by HT alone was the most common sequence. After the first regimen, 52% of patients reused the same anti-HER2 drugs in the second regimen, 21% added another anti-HER2 drug and 27% switched to a different anti-HER2 regimen. After the second regimen, 14% reused anti-HER2 drugs and 6% added another anti-HER2 drug, 25% switched to a different anti-HER2 regimen; 15% reused anti-HER2 drugs from the first regimen.

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Utilization of anti-HER2 regimens among HER2-positive metastatic breast cancer patients.