Combination Therapy of Pyrotinib and Metronomic Vinorelbine in HER2+ Advanced Breast Cancer After Trastuzumab Failure (PROVE): A Prospective Phase 2 Study.

Purpose: Approximately 50-74% of patients with metastatic HER2-positive breast cancer do not respond to trastuzumab, with 75% of treated patients experiencing disease progression within a year. The combination of pyrotinib and capecitabine has showed efficacy in these patients. This study evaluates the efficacy and safety of pyrotinib combined with metronomic vinorelbine for trastuzumab-pretreated HER2-positive advanced breast cancer patients.

Materials and methods: In this phase 2 trial, patients aged 18-75 years with HER2-positive advanced breast cancer who had previously failed trastuzumab treatment were enrolled to receive pyrotinib 400mg daily in combination with vinorelbine 40mg thrice weekly. The primary endpoint was progression-free survival (PFS), while secondary endpoints included objective response rate (ORR), disease control rate (DCR), overall survival (OS), and safety.

Results: From October 21, 2019, to January 21, 2022, 36 patients were enrolled and received at least one dose of study treatment. At the cut-off date, 20 experienced disease progression or death. With a median follow-up duration of 35 months, the median PFS was 13.5 months (95% CI: 8.3-18.5). With all patients evaluated, an ORR of 38.9% (95% CI: 23.1-56.5%) and a DCR of 83.3% (95% CI: 67.2-93.6%) were achieved. The median OS was not reached. Grade 3 adverse events (AEs) were observed in 17 patients, with diarrhea being the most common (27.8%), followed by vomiting (8.3%) and stomachache (5.6%). There were no grade 4/5 AEs.

Conclusion: Pyrotinib combined with metronomic vinorelbine showed promising efficacy and an acceptable safety profile in HER2-positive advanced breast cancer patients after trastuzumab failure.