Subcutaneous trastuzumab with pertuzumab and docetaxel in HER2-positive metastatic breast cancer: Final analysis of MetaPHER, a phase IIIb single-arm safety study

PURPOSE: Intravenous trastuzumab, pertuzumab, and docetaxel are first-line standard of care for patients with HER2-positive metastatic breast cancer (mBC). MetaPHER is the first study assessing the safety and tolerability of subcutaneous trastuzumab plus intravenous pertuzumab and chemotherapy in a global patient population with HER2-positive mBC. METHODS: In this open-label, single-arm, multicenter, phase 3b study, eligible patients were ≥ 18 years old with histologically/cytologically confirmed previously untreated HER2-positive mBC. All received ≥ 1 subcutaneous trastuzumab 600 mg fixed dose plus intravenous pertuzumab (loading dose: 840 mg/kg; maintenance: 420 mg/kg) and docetaxel (≥ 6 cycles; initial dose 75 mg/m(2)) every 3 weeks. The primary objective was safety and tolerability; secondary objectives included efficacy. RESULTS: At clinical cutoff, 276 patients had completed the study; median duration of follow-up was 27 months. The most common any-grade adverse events were diarrhea, alopecia, and asthenia; the most common grade ≥ 3 events were neutropenia, febrile neutropenia, and hypertension. There were no cardiac deaths and mean left ventricular ejection fraction was stable over time. Median investigator-assessed progression-free survival was 18.7 months; objective response rate was 75.6%. CONCLUSIONS: Safety and efficacy with subcutaneous trastuzumab plus intravenous pertuzumab and docetaxel in mBC are consistent with historical evidence of intravenous trastuzumab with this combination. Findings further support subcutaneous administration not affecting safety/efficacy profiles of trastuzumab in HER2-positive BC with increased flexibility in patient care. A fixed-dose combination of pertuzumab and trastuzumab for subcutaneous injection has recently been approved for the treatment of HER2-positive early/mBC, further addressing the increasing relevance of and need for patient-centric treatment strategies. TRIAL REGISTRATION: NCT02402712 SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s10549-021-06145-3.