Stromal NNMT Overexpression As an Independent Prognostic Biomarker in Lung Adenocarcinoma and Breast Carcinoma

This study investigated the expression profile and prognostic significance of nicotinamide N-methyltransferase (NNMT) in pan-cancer stroma, with focused validation in lung adenocarcinoma (LUAD) and breast carcinoma (BC). Integrated analysis of Genotype-Tissue Expression and The Cancer Genome Atlas databases revealed tumor-specific NNMT mRNA upregulation in these malignancies. Subsequently, the relationship between NNMT mRNA expression levels and clinical parameters across multiple cancer types was examined, with particular emphasis on LUAD, BC, and CRC. Single-cell RNA sequencing data further revealed elevated NNMT expression specifically within stromal compartments, with fibroblasts exhibiting the highest NNMT expression levels among stromal cell populations. Protein-level validation using the Human Protein Atlas database, the National Cancer Institute's Proteomics Data Commons, and the quantitative immunohistochemistry of our independent clinical cohorts demonstrated elevated stromal NNMT protein expression, particularly in cancer-associated fibroblasts. Cox regression analysis and survival curve analysis established stromal NNMT expression as an independent prognostic factor for overall survival in LUAD and BC patients (P < .05). In conclusion, high stromal NNMT levels correlated with poor prognosis, establishing it as a promising biomarker for risk stratification in LUAD and BC.