The efficacy of pyrotinib-based therapy in lapatinib-resistant metastatic HER2-positive breast cancer

Background: Human epidermal growth factor receptor 2 (HER2 )-positive breast cancer tends to metastasize and is associated with poor prognosis. Anti-HER2 treatment combined with chemotherapy or endocrine therapy is often used for HER2-positive metastatic breast cancer (MBC). For later lines of therapy in HER2-positive MBC, there is no standard treatment. We investigated the efficacy of pyrotinib, a new irreversible tyrosine kinase inhibitor (TKI) targeting epidermal growth factor receptor, HER2 , and HER4 , in lapatinib-resistant HER2-positive MBC patients. Methods: This is a retrospective observational study including lapatinib-resistant HER2-positive MBC patients who received pyrotinib-based treatment. We used the Kaplan-Meier method for the survival analyses. Results: A total of 31 patients were included. Concurrent treatments included cytotoxic chemotherapy (29 patients, 93.6%), endocrine therapy (1 patient, 3.2%), and another targeted therapy (1 patient, 3.2%). The objective response rate (ORR) was 25.8% and the median progression-free survival in the study population was 4.5 months (95% CI: 3.1-5.9 months). The treatment-related adverse events (AEs) included diarrhea, neutropenia, vomiting, fatigue, and thrombocytopenia. Dose reduction to 320 mg was conducted in 19.4% of all cases due to severe AEs. Conclusions: Pyrotinib-based treatment was effective and generally well tolerated in lapatinib-resistant HER2-positive MBC for later line treatment.