High stromal nicotinamide N‐methyltransferase (NNMT) indicates poor prognosis in colorectal cancer

PURPOSE: Nicotinamide n‐methyltransferase (NNMT) has good biochemical activity and epigenetic regulation, and has been reported as a major metabolic regulator of cancer. The goal of this study was to investigate the significance of stromal NNMT expression in colorectal cancer (CRC). PATIENTS AND METHODS: Stromal expression of NNMT in primary CRC, metastasis CRC, and their non‐cancerous tissues from 1088 CRC patients was examined by immunohistochemistry. The associations between stromal NNMT expression and survival outcomes in 967 patients with stage I‐III CRC were further evaluated with Kaplan‐Meier curve and Cox model analyses. RESULTS: NNMT expression was mainly sourced from stromal compartments and also elevated in CRC. Patients with high stromal NNMT (IHC‐score ≥ 106) have a worse survival than those patients with low stromal NNMT. In multiple Cox analyses, high expression of stromal NNMT remained as an independent risk factor in CRC for disease‐free survival with a hazard ratio (HR) of 1.415 (95% confidence interval [CI], 1.015‐1.972) and disease‐specific survival with a HR of 5.004 (95% CI, 2.301‐10.883). In addition, high stromal NNMT expression in CRC also indicates the poor survival outcomes in patients with early stage CRC (stage I and II) and in patients who undergo chemotherapy. CONCLUSION: NNMT is mainly located in CRC stromal compartment. High stromal NNMT expression predicts an unfavorable postoperative prognosis.