Expression and clinical significance of nicotinamide n-methyltransferase in cervical squamous cell carcinoma

Nicotinamide N-methyltransferase (NNMT) is a cytosolic enzyme, overexpressed in various human malignancies. It is associated with cancer progression and resistance to treatment. The role of NNMT in cervical cancer has not been studied thus far. We aimed to evaluate expression of NNMT in cervical squamous cell carcinoma (SCC) and investigate its clinical significance. NNMT expression was assayed by use of immunohistochemistry in 61 cases of SCC, 11 cases of high-grade squamous intraepithelial lesion, 17 cases of low-grade squamous intraepithelial lesion, and 51 benign cervical tissues. NNMT immunoreactivity was scored based on staining intensity and percentage of positively stained cells. The expression of NNMT was significantly higher in SCC than in benign tissue, low-grade squamous intraepithelial lesion, and high-grade squamous intraepithelial lesion (P<0.001). NNMT expression in benign tissue was significantly lower than in low-grade squamous intraepithelial lesion and high-grade squamous intraepithelial lesion. When stratified according to stage, NNMT expression was significantly higher in patients with stage III and IV than those in stage I and II disease (P=0.009). For all stages, patients with metastatic pelvic or para-aortic lymph nodes had significantly higher NNMT expression than patients without nodal involvement (P=0.001). Although preliminary, this is the first study to detect overexpression of NNMT in SCC and increased expression associated with advanced stage and metastatic lymph nodes. NNMT should be investigated further in cervical cancer as a potential therapeutic target and a prognostic indicator.