Pathological response and predictive role of tumour-infiltrating lymphocytes in HER2-positive early breast cancer treated with neoadjuvant pyrotinib plus trastuzumab and chemotherapy (Panphila): a multicentre phase 2 trial

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.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.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.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.