Tumor-Infiltrating Mast Cells Enhance Neoadjuvant Therapy Efficacy in ESCC via Modulation of the Desmoplastic Microenvironment.

OBJECTIVE: Neoadjuvant therapy is essential for locally advanced esophageal squamous cell carcinoma (ESCC), but its efficacy requires improvement. This study investigated the role of tumor-infiltrating mast cells (MCs) in treatment response and prognosis. METHODS: An integrated approach was employed, combining single-cell RNA sequencing of paired specimens from one ESCC patient pre- and post-neoadjuvant therapy, immunofluorescence analysis of a retrospective cohort of 68 treatment-naïve ESCC surgical specimens, bioinformatics analysis of public datasets, and in vitro mast cell activation assays. RESULTS: Single-cell sequencing revealed a post-therapy increase in the proportion of MCs among immune cells (4% to 12%), alongside an enriched inflammatory gene profile. In the cohort of 68 patients, higher MC density was associated with smaller tumor diameter (Pearson r = -0.32, p=0.007) and significantly better overall survival (36 vs 23.5 months, p=0.038). No such correlations were found for macrophages or CD8+ T cells. Bioinformatic analysis linked MCs to extracellular matrix and vascular smooth muscle regulation. Critically, high MC density combined with low desmoplasia or fibrosis identified patients with the most favorable prognosis. Phenotypically, MCs were predominantly non-degranulated in situ. In vitro, LPS activation (a non-degranulating signal) significantly upregulated CCL19 and other chemokines in mast cells. Furthermore, LPS was detected in the tumor stroma of 47.1% (32/68) of patients but not in normal mucosa. CONCLUSION: The findings demonstrate that tumor-infiltrating MCs are associated with enhanced efficacy of neoadjuvant therapy and improved survival in ESCC. The mechanism may involve LPS-induced, non-degranulatory MC activation that modulates the desmoplastic microenvironment. Targeting this axis presents a promising strategy for ESCC treatment.