Rationale and design of a phase II trial of pyrotinib in combination with nab-paclitaxel as adjuvant therapy for N0/N1mi, HER2 + early breast cancer (PHAEDRA).

<bold>Background: </bold>The de-escalation treatment in patients with low-risk HER2-positive early breast cancer (eBC) is an attractive strategy to avoid unnecessary treatment and improve the quality of life of patients. Pyrotinib, a novel irreversible pan-HER2 tyrosine kinase inhibitor (TKI), has shown efficacy in patients with advanced HER2-positive breast cancer. Meanwhile, nanoparticle albumin-bound (nab)-paclitaxel reveals survival benefit over solvent-based paclitaxel and eliminates the toxicities associated with the solvent. However, the efficacy and safety of pyrotinib in combination with nab-paclitaxel as adjuvant therapy for low-risk HER2 + eBC patients have not been evaluated.<bold>Methods: </bold>This is a multicenter, open-label, single-arm phase II study. A sample size of 261 patients with tumor ≤ 3 cm, lymph node-negative (N0) or micrometastatic (N1mi), HER2 + breast cancer will be recruited. Eligible patients will receive nab-paclitaxel 260 mg/m2 once every 3 weeks for 12 weeks and pyrotinib 400 mg once daily for one year. The primary endpoint is invasive disease-free survival. A sub-study will be conducted to investigate different prophylactic strategies for diarrhea, which is the most common adverse event of pan-HER TKIs. One hundred and twenty patients from the main study will be randomly (1:1) allocated to receive loperamide either during the first cycle (4 mg tid on days 1-7, then 4 mg bid on days 8-21) or the first 2 cycles (4 mg tid on days 1-7, then 4 mg bid on days 8-42). The primary endpoint of the sub-study is the incidence of grade ≥ 3 diarrhea.<bold>Discussion: </bold>This is the first prospective study of pyrotinib in combination with nab-paclitaxel as adjuvant therapy for patients with low-risk HER2-positive eBC. It would probably provide robust evidence for de-escalating strategy of HER2-positive eBC and appropriate management for pyrotinib-related diarrhea.<bold>Trial Registration: </bold>ClinicalTrials.gov Identifier: NCT04659499 . Registered on December 9, 2020. [ABSTRACT FROM AUTHOR]