Immune Cell Infiltration Characteristics in the Tumor Microenvironment of Triple-Negative Breast Cancer and Their Prognostic Value

Yun Liu （ The Sixth Medical Center of the PLAGeneral Hospital, Beijing 100000, China ）

Abstract

Triple-negative breast cancer (TNBC) is characterized by the absence of estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2) expression, rendering endocrine therapy and anti-HER2 targeted therapy inefective. As a result, therapeutic options for TNBC are limited, and the prognosis remains poor. In recent years, with the successful application of immunotherapy in various solid tumors, TNBC—recognized as the most immunogenic subtype of breast cancer—has attracted increasing attention, particularly regarding the immune cell infiltration patterns within its Tumor Microenvironment (TME). This review systematically summarizes the composition, functional states, spatial distribution, and interaction networks of key immune cell populations in the TNBC TME, including tumor-
infiltrating lymphocytes (TILs), myeloid-derived suppressor cells (MDSCs), tumor-associated macrophages (TAMs), and regulatory T cells (Tregs). Furthermore, it comprehensively discusses the associations between these immune infiltration characteristics and clinicopathological features, therapeutic responses, and long-term survival outcomes of patients. This review aims to provide a theoretical basis and novel insights for the development of precision immunotherapy strategies in TNBC.

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