De-escalated neoadjuvant pertuzumab plus trastuzumab therapy with or without weekly paclitaxel in HER2-positive, hormone receptor-negative, early breast cancer (WSG-ADAPT-HER2+/HR-): survival outcomes from a multicentre, open-label, randomised, phase 2 trial

Background Several de-escalation neoadjuvant strategies have been investigated to reduce the use of chemotherapy in HER2-positive early breast cancer using pathological complete response as a surrogate endpoint; there are few survival data from these trials. Here, we report 5-year survival data in the WSG-ADAPT-HER2+/HR- trial and address the effect of pathological complete response, early therapy response, and molecular subtype. Methods WSG-ASAPT-HER2+/ HR-, a part of the ADAPT umbrella trial performed in patients with different subtypes of early breast cancer, was an investigator-initiated, multicentre, open-label, randomised, phase 2 trial done at 40 Breast Cancer Centres in Germany. Eligible patients were aged 18 years or older with histologically confirmed, unilateral, primary invasive, non-inflammatory early breast cancer, hormone receptor-negative and HER2-positive status, and an Eastern Cooperative Oncology Group performance status of 0 or 1 or a Karnofsky performance status of at least 80%. Patients were randomly assigned (5:2, block size 21, stratified by centre and clinical nodal status) to 12 weeks of either trastuzumab (8 mg/kg loading dose, then 6 mg/kg every 3 weeks) plus pertuzumab (840 mg loading dose, then 420 mg every 3 weeks) or trastuzumab plus pertuzumab plus paclitaxel (80 mg/m (2) weekly); all drugs were administered intravenously. The primary objective of the trial was to compare the number of patients with a pathological complete response at surgery (ie, no invasive tumour cells in breast and lymph nodes [ypT0/is ypN0], the primary endpoint) in early responders (ie, low cellularity or Ki67 decrease =30% after 3 weeks) in the trastuzumab plus pertuzumab group versus all patients (irrespective of an early response) in the trastuzumab plus pertuzumab plus paclitaxel group. Non-inferiority was defined as a pathological complete response no worse than 23% lower in the early-responder proportion of patients in the trastuzumab plus pertuzumab grou