Pyrotinib plus capecitabine versus lapatinib plus capecitabine for the treatment of HER2-positive metastatic breast cancer (PHOEBE): a multicentre, open-label, randomised, controlled, phase 3 trial

Background: Despite therapeutic advances in HER2-positive metastatic breast cancer, resistance to trastuzumab inevitably develops. In the PHOEBE study, we aimed to assess the efficacy and safety of pyrotinib (an irreversible pan-HER inhibitor) plus capecitabine after previous trastuzumab. Methods: This is an open-label, randomised, controlled, phase 3 trial done at 29 hospitals in China. Patients with pathologically confirmed HER2-positive metastatic breast cancer, aged 18–70 years, who had an Eastern Cooperative Oncology Group performance status of 0 or 1, and had been previously treated with trastuzumab and taxanes were randomly assigned (1:1) to receive oral pyrotinib 400 mg or lapatinib 1250 mg once daily plus oral capecitabine 1000 mg/m² twice daily on days 1–14 of each 21-day cycle. Randomisation was done via a centralised interactive web-response system with a block size of four or six and stratified by hormone receptor status and previous lines of chemotherapy for metastatic disease. The primary endpoint was progression-free survival according to masked independent central review. Efficacy and safety were assessed in all patients who received at least one dose of the study drugs. Results presented here are from a prespecified interim analysis. This study is registered with ClinicalTrials.gov, NCT03080805. Findings: Between July 31, 2017, and Oct 30, 2018, 267 patients were enrolled and randomly assigned. 134 patients received pyrotinib plus capecitabine and 132 received lapatinib plus capecitabine. At data cutoff of the interim analysis on March 31, 2019, median progression-free survival was significantly longer with pyrotinib plus capecitabine (12·5 months [95% CI 9·7–not reached]) than with lapatinib plus capecitabine (6·8 months [5·4–8·1]; hazard ratio 0·39 [95% CI 0·27–0·56]; one-sided p<0·0001). The most common grade 3 or worse adverse events were diarrhoea (41 [31%] in the pyrotinib group vs 11 [8%] in the lapatinib group) and hand–foot syndrome (22 [16%] vs 20 [15%]). Serious adverse events were reported for 14 (10%) patients in the pyrotinib group and 11 (8%) patients in the lapatinib group. No treatment-related deaths were reported in the pyrotinib group and one sudden death in the lapatinib group was considered treatment related. Interpretation: Pyrotinib plus capecitabine significantly improved progression-free survival compared with that for lapatinib plus capecitabine, with manageable toxicity, and can be considered an alternative treatment option for patients with HER2-positive metastatic breast cancer after trastuzumab and chemotherapy. Funding: Jiangsu Hengrui Medicine and National Key R&D Program of China. Translations: For the Chinese translation of the abstract see Supplementary Materials section.