Pyrotinib and trastuzumab plus palbociclib and fulvestrant in HR+/HER2+ breast cancer patients with brain metastasis

Abstract Human epidermal growth factor receptor 2-positive (HER2+) breast cancer (BC) patients are at a high risk of developing metastases in the brain. However, research focusing on treatment strategies for hormonal receptor positive (HR+), HER2+ BC patients with brain metastases (BM) remains limited. Thus, a multi-center, prospective trial was conducted in China. Women over the age of 18 who were naive to whole brain radiotherapy and had estrogen receptor (ER)/progesterone-receptor (PgR) positive, HER2+ BM were treated with palbociclib, fulvestrant, trastuzumab and pyrotinib, until disease progression or the development of intolerable side effects. The primary endpoint was objective response rate (ORR) in the central nervous system (CNS). This ongoing study is still recruiting participants and is registered with ClinicalTrials.gov (NCT04334330). This report presents the findings from an interim analysis. From December 4, 2020, to November 2, 2022, 15 patients were enrolled. Among the 14 patients who were evaluable for clinical response, the ORR was 35.7% (95% CI: 12.8–64.9%), with a CNS–ORR of 28.6% (95% CI: 8.4–58.1%). The median follow-up period was 6.3 months (range, 2.1–14.3 months), during which the median progression-free survival (PFS) was 10.6 months (95% CI: 4.3–16.9 months), and the median time to CNS progression was 8.5 months (95% CI: 5.9–11.1 months). The most common adverse event was diarrhea (93%), with 33% having grade 3 and 6.7% having grade 4. The study suggests that the combination of palbociclib, trastuzumab, pyrotinib and fulvestrant offers a promising chemo-free treatment strategy for HR+, HER2+ BC patients with BM.