Overexpression of TFF3 is Associated with Immune Infiltration, Molecular Subtypes, and Clinical Progression in Breast Cancer.

[OBJECTIVE] Trefoil factor 3 (TFF3), a secreted protein involved in mucosal protection and tumor progression, has an incompletely defined role in breast cancer (BRCA). This study aimed to comprehensively evaluate TFF3 expression patterns, clinical relevance, and prognostic significance in BRCA.

[METHODS] Data from the TCGA, GTEx, TNMplot, and TISCH2 databases were integrated to analyze TFF3 expression and clinical significance. Protein expression in clinical samples was validated via immunohistochemistry (IHC), and survival analysis, immune infiltration assessment, and functional enrichment analyses were performed to explore the biological role of TFF3.

[RESULTS] TFF3 was significantly upregulated in BRCA tumor tissues compared with normal tissues (P < 0.001) and was expressed predominantly in malignant cells and tumor-associated macrophages. High TFF3 expression correlated strongly with hormone receptor (estrogen receptor/progesterone receptor) positivity, luminal A/B subtypes, and early-stage disease (P < 0.01) and showed excellent diagnostic performance for distinguishing basal-like from non-basal-like BRCA (AUC = 0.95). TFF3 was an independent protective factor: high expression was associated with improved overall survival (HR = 0.75, P = 0.02) and disease-free survival (P < 0.001), especially in patients receiving hormone therapy (HR = 0.89, P = 0.0002) or chemotherapy (HR = 0.89, P = 0.0002). TFF3 exhibited immunomodulatory properties, correlated positively with M2 macrophages and negatively with cytotoxic immune cells (CD8 T cells, NK cells) and checkpoint molecules (PD-1, CTLA-4) (P < 0.01). Functional analyses linked TFF3 to estrogen response pathways and cell cycle regulation. IHC validation confirmed TFF3 overexpression in 78.1% of tumors versus 23.9% of normal tissues (P < 0.001), with the lowest expression in the basal-like subtype (8.33% vs. 59.2%, P = 0.0007).

[CONCLUSIONS] TFF3 is a robust diagnostic biomarker for BRCA molecular subtyping, an independent prognostic factor, and a potential immunomodulator. These findings highlight its clinical utility for patient stratification and potential as a therapeutic target, particularly in hormone receptor-positive BRCA.