297PLack of benefit of neoadjuvant pertuzumab in high risk HER2 positive breast cancer: A retrospective case-control study of 355 cases with biomarker analysis

Abstract Background The NEOSPHERE trial suggested that pertuzumab (P) added to a combination of docetaxel and trastuzumab (T) as a neoadjuvant therapy in HER2 positive breast cancer (HER2+ BC) patients (pts) significantly enhances pathological complete response (pCR) rates. Here, we report our institution experience, focusing on stage III tumors. Methods We reviewed clinical and pathological response (residual cancer burden, RCB) in 355 HER2+ BC treated between 2010 and 2017 with neoadjuvant chemotherapy combined with T (n = 291) or TP (n = 64). Results were adjusted according to clinical stage, hormone receptors (HR) status, and chemotherapy regimen. In a subset of 157 pts matched on clinical TNM stage and HR expression (T, n = 98; TP, n = 59), a baseline pathological biomarker analysis was performed to assess TILs, PTEN, FOXP3 and PD-L1 expression. Results Among 355 patients, tumor clinical stages were T3 -T4 for 40% vs. 72% of T and TP pts (p  Conclusions This retrospective study did not suggest any benefit of neoadjuvant TP dual HER2 blockade regarding pathological response for stage III HER2+ BC. Baseline pathological expressions of PTEN, FOXP3, TILs, PD-L1 did not correlate with pathological response. Legal entity responsible for the study Institut Curie. Funding Institut Curie. Disclosure All authors have declared no conflicts of interest.