Abstract P4-04-06: Immune balance between tumor-infiltrating lymphocytes and tumor-associated macrophages impacts the outcome of triple negative breast cancer patients
Authors: Bottai G , Raschioni C , Losurdo A , Di Tommaso L , Roncalli M , Santarpia L 
Published: May 2016

Background: Stromal tumor-infiltrating lymphocytes (TILs) are emerging as a robust prognostic factor in triple negative breast cancer (TNBC). However, the prognostic value of TILs may be also influenced by the complex landscape of the tumor immune microenvironment. In this study, we aimed to assess the correlation between TILs and tumor-associated macrophages with pro-tumoral functions (M2 TAMs), and to determine the prognostic role of TAM/TIL ratio in TNBC.

Methods: Formalin-fixed, paraffin-embedded tissues were retrospectively collected from 189 patients with histologically confirmed invasive ductal TNBC. Stromal TILs were evaluated on H&E slides. The content of CD163-positive M2 TAMs in tumor stroma was assessed by immunohistochemistry. Whole tumor slides were independently assessed by two pathologists blinded for patient characteristics and outcome. CD163 staining was dichotomized into absent/moderate or dense infiltration; 50% stromal TILs was used as threshold (Salgado, 2015). Statistical analyses were performed using Spearman's correlation, Fisher's exact tests, Kaplan-Meier and Cox regression analyses.

Results: TNBC patients treated with adjuvant chemotherapy who experienced tumor recurrence showed a significant lower content of stromal TILs (p &lt; 0.0001) and a higher infiltration of CD163-positive TAMs (p = 0.020) compared to patients without recurrence. Stromal TILs were also associated with lymph node positivity (p = 0.036). Univariate and multivariate analysis confirmed the importance of stromal TILs as a prognostic marker of recurrence-free survival (RFS), and overall survival (OS). Importantly, we found that stromal TILs inversely correlated with CD163-positive TAMs (rs = -0.539; p &lt; 0.0001), indicating the significance of the balance between distinct immune components in the tumor microenvironment. Consistently, TNBC patients with a high TAM/TIL ratio had significantly shorter RFS (Log-rank p &lt; 0.0001) and OS (Log-rank p &lt; 0.0001) than patients with low TAM/TIL ratio. TAM/TIL ratio also retained its independent prognostic significance for RFS (HR = 7.02; 95%CI 2.09 - 23.59, p = 0.002) and OS (HR = 7.11; 95%CI 2.10 - 24.05, p = 0.002) in multivariate analysis.

Conclusions: Distinct immune cell subpopulation may have a specific role in modulating the immune response against breast tumor. A high content of TAMs with pro-tumoral functions may influence the recruitment of lymphocytes and suppress antitumor immunity. Indeed a high TAM/TIL ratio could help to identify a subset of TNBC patients at high risk for relapse and reduced OS. The understanding of the biological and clinical relevance of immune balance in tumor microenvironment warrants further investigations, and may be useful for the stratification of TNBC patients who may benefit from the addition of immunomodulatory therapies.

Citation Format: Bottai G, Raschioni C, Losurdo A, Di Tommaso L, Roncalli M, Santarpia L. Immune balance between tumor-infiltrating lymphocytes and tumor-associated macrophages impacts the outcome of triple negative breast cancer patients. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P4-04-06.