Dissecting the Non-Immune Tumor Microenvironment in Triple-Negative Breast Cancer: Molecular Subtype-Specific Patterns and Prognostic Implications

Triple-Negative Breast Cancer (TNBC) encompasses a biologically heterogeneous group of tumors, which can be classified into distinct molecular subtypes, namely basal-like 1 (BL1), basal-like 2 (BL2), immunomodulatory (IM), mesenchymal (M), mesenchymal stem-like (MSL), and luminal androgen receptor (LAR), with unique clinical and pathological characteristics. While immune features of these subtypes have been extensively characterized, the integration of non-immune stromal and structural components into our understanding of TNBC biology is only now being fully recognized. This narrative review synthesizes current evidence regarding differences in the non-immune microenvironment across TNBC molecular subtypes, with a focus on cancer-associated fibroblasts (CAFs), vascular features, extracellular matrix (ECM) dynamics, and epithelial–mesenchymal transition (EMT), along with metabolic–hypoxic reprogramming. Data from several studies are integrated to highlight subtype-specific signatures. Differences in stromal architecture and metabolic adaptations, potentially reflecting the underlying molecular heterogeneity, may hold prognostic or predictive significance and could inform personalized therapeutic strategies targeting the tumor–stroma interface.