PTGER4 and metastatic malignant neoplasm in the lymph nodes: Among different pathologic types, LC patients with TNM stage IV had the highest positive rate of PTGER4 gene methylation (P < 0.05); the positive rate of PTGER4 gene methylation was comparedamong different ages, genders, with or without smoking history, and among LC patients with different pathologic types, tissue differentiation, maximum tumor diameter, and lymph node metastasis, and the difference was not statistically significant (P > 0.05).