The results showed that the concentration of cfDNA was significantly correlated with the levels of CEA, CA199, CA125, NSE, LDH and the sum of tumor diameters, especially CEA (P < 0.0001, Pearson r = 0.81), LDH (P < 0.0001, Pearson r = 0.84) and the sum of tumor diameters (P < 0.0001, Pearson r = 0.80). The gene discussed is ENO2; the disease is neoplasm.