Evaluation Of Tumor Immune Infiltrate As A Determinant Of Response To Neo-Adjuvant Lapatinib And Trastuzumab (Lt) In Her2-Positive (+) Breast Cancer (Bc).

608Background: Dual HER2 blockade with LT without chemotherapy resulted in a substantial pathologic complete response (pCR) rate in HER2+ BC patients (pts) (TBCRC006). High levels of tumor infiltrating lymphocytes (TILs) at diagnosis have shown to be associated with greater benefit to T and chemotherapy in early-stage HER2+ BC pts. However the predictive value of TILs, TILs’ subsets, and other immune cells in pts receiving anti-HER2 treatment alone without chemotherapy is still unknown. Methods: Pre-treatment biopsies from pts enrolled in the TBCRC006 trial were used to investigate tumor immune infiltrate at diagnosis. Hematoxylin and eosin (HE a threshold of 60% was used to define lymphocyte-predominant BC (LPBC). Single formalin-fixed paraffin-embedded slides from 10 cases were co-stained for CD4, CD8, CD20, CD68, FoxP3, cytokeratin, and DAPI by multiplexed immunofluorescence (m-IF) using Perkin...