For serum tumor markers, all NET patients (17/17, 100%) have normal CEA, while only 69.8% of NEC patients (37/53) have normal CEA, and the difference between them was statistically significant (P=0.008) (Table 2).We also find that the expression level of CA125 was increased in 4 patients and the expression level of AFP was increased in 3 patients, all of whom were NEC patients, but the results were not statistically different. Here, CEACAM5 is linked to neuroendocrine carcinoma.