Phase II neoadjuvant pyrotinib combined with epirubicin and cyclophosphamide followed by docetaxel in HER2-low–expressing and HR-positive early or locally advanced breast cancer (PILHLE-001): A single-arm trial.

TPS620 Background: As a latent new subtype, HER2-low-expressing breast cancer has attracted increasing attention. However, HER2-low-expressing/HR-positive early or locally advanced breast cancer (E/LABC) has the lowest pathological complete response (pCR) rate among all types of breast cancer. Pyrotinib, a small-molecule HER1/HER2/HER4 tyrosine kinase inhibitor, combined with chemotherapy regimen showed excellent efficacy and safety in the treatment of patients with HER2-positive early, locally advanced and metastatic breast cancer. In-vitro experiment showed pyrotinib can significantly inhibit colony formation in breast cancer cell lines with different HER2 expression levels including HER2-positive and HER2-low-expressimg [immunohistochemistry (IHC) 2+/in situ hybridization (ISH) negative]. Therefore, the investigator-driven, ongoing PILHLE-001 trial has been conducted to evaluate the potential role of neoadjuvant pyrotinib plus chemotherapy in the treatment of HER2-low-expressing/HR-positive E/LABC, which may provide a novel neoadjuvant therapeutic strategy for these patients. Methods: PILHLE-001, as a single-arm, phase Ⅱ study, is the first trial to evaluate the efficacy and safety of neoadjuvant pyrotinib combine with chemotherapy in HER2-low-expressing (defined as IHC 2+ with ISH negative) and HR-positive (ER or PR > 1% stained cells) E/LABC (cT1c with histologically involved lymph nodes or ≥cT2). Patients who have HER2 IHC 1+, or severe heart diseases or basic gastrointestinal diseases are excluded. The trial has 80% power to detect true difference from previous reported pCR rate of 17.5%, to an expected pCR rate of 35% at two-sided alpha level of 0.05. Considering a drop rate of 10%, a total of 46 patients will be needed. Since May 19, 2021 until now, 19 patients have been enrolled. All eligible patients will receive pyrotinib 320mg orally daily with all chemotherapy cycles (epirubicin 90 mg/m² intravenously plus cyclophosphamide 600 mg/m² intravenously on day 1 for four 3-week cycles followed by docetaxel 100 mg/m² intravenously on day 1 for four 3-week cycle). The primary outcome is the rate of total pCR, defined as no residual invasive tumor cells in the breast and axillary nodes, regardless of ductal carcinoma in situ (ypT0/is ypN0) after neoadjuvant treatment. The secondary outcomes include Miller-Payne grade, residual cancer burden score, overall response rate, breast conservation rate, disease-free survival, overall survival, exploratory biomarkers and drug related safety. Primary efficacy outcomes will be analyzed in the intention‐to‐treat population and safety outcomes in the safety set population. Long-term efficacy outcomes will be assessed later with enough follow-up. Clinical trial information: NCT05165225.