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PURPOSE Panphila evaluated pyrotinib plus trastuzumab, docetaxel and carboplatin as neoadjuvant therapy for early breast cancer (BC), and investigated the predictive role of immune cell subpopulations. PATIENTS AND METHODS In this multicentre phase 2 study, patients with human epidermal growth factor receptor 2-positive, stage T2-3N0-3M0 BC received pyrotinib 400 mg once daily plus docetaxel (75 mg/m2, day 1), carboplatin (6 mg/mL/min, day 1) and trastuzumab (8 mg/kg loading dose and 6 mg/kg maintenance dose, day 1) for 6 cycles of 21 days each. Simon's 2-stage design was adopted. The primary end-point was pathological complete response (pCR, ypT0/is ypN0) rate. Tumour-infiltrating lymphocytes (TILs) were assessed by haematoxylin and eosin staining and multiplex immunohistochemistry. RESULTS In the modified intention-to-treat population (n = 69), 38 patients (55.1%) achieved pCR. In the safety population (n = 74), the most common grade ≥3 adverse events were diarrhoea (43.2%), anaemia (37.8%), vomiting (16.2%) and platelet count decrease (10.8%). No treatment-related deaths occurred. Analysis of single immune subpopulations revealed a significant association of pCR with higher baseline infiltration by stromal (s)-CD20+, s-CD8+ and s-CD4+ TILs. Unsupervised hierarchical clustering of stromal immune markers identified a group of patients characterised by high s-CD20+, s-CD8+, s-CD4+ and s-FOXP3+ immune cells infiltration, which was independently associated with pCR. CONCLUSION Neoadjuvant pyrotinib plus trastuzumab-based chemotherapy exhibits promising efficacy and manageable toxicity in patients with human epidermal growth factor receptor 2-positive early BC, and thus phase 3 trials are warranted. Our findings also contribute to understanding the potential role of the immune microenvironment in response to neoadjuvant pyrotinib-based therapy.