Evaluation of the predictive role of tumor immune infiltrate in HER2-positive breast cancer patients treated with neoadjuvant anti-HER2 therapy without chemotherapy

Purpose: Tumor infiltrating lymphocytes (TILs) are associated with benefit to trastuzumab and chemotherapy in early-stage HER2+ breast cancer (BC) patients. The predictive value of TILs, TIL subsets, and other immune cells in patients receiving chemotherapy-sparing lapatinib plus trastuzumab (LT) treatment is unclear. Experimental Design: H&E-stained slides (n=59) were used to score stromal (s-)TILs from pre-treatment biopsies of patients enrolled in the neoadjuvant TBCRC006 trial of 12-week LT therapy (plus endocrine therapy for ER+ tumors). A 60% threshold was used to define lymphocyte-predominant BC (LPBC). Multiplexed immunofluorescence (m-IF) staining (CD4, CD8, CD20, CD68, and FoxP3) and multispectral imaging were performed to characterize immune infiltrates in single FFPE slides (n=33). Results: The pathologic complete response (pCR) rate was numerically higher in LPBC patients compared to non-LPBC patients (50% vs. 19%, P=0.057). Unsupervised hierarchical clustering of the five immune markers identified two patient clusters with different responses to LT treatment (pCR = 7% vs. 50%, for Cluster 1 vs. 2 respectively, P=0.01). In multivariable analysis, Cluster 2, characterized by high CD4+, CD8+, CD20+ s-TILs, and high CD20+ intratumoral TILs, was independently associated with a higher pCR rate (P=0.03). Analysis of single immune subpopulations revealed a significant association of pCR with higher baseline infiltration by s-CD4, intratumoral (i-) CD4, and i-CD20+ TILs. Conclusions: LPBC was marginally associated with higher pCR rate than non-LPBC in LT treated HER2+ BC patients. Quantitative assessment of the immune infiltrate by m-IF is feasible and may help correlate individual immune cell subpopulations and immune cell profiles with treatment response.