Abstract: Objective To study the significance of serum carcinoembryonic antigen (CEA) and procalcitonin (PCT) levels before and after radical surgery for medullary thyroid carcinoma (MTC). Methods The clinicopathological data and follow-up data of 80 MTC patients who underwent radical surgery in our hospital from January 2020 to January 2023 were retrospectively analyzed, and the relationship between serum CEA and PCT levels and preoperative pathological characteristics was analyzed. The predictive efficacy of CEA and PCT for MTC lymph node metastasis was analyzed by receiver operating characteristic curve (ROC). According to the postoperative follow-up, patients were divided into cure group and recurrence/metastasis group, and the serum CEA and PCT levels of the two groups were compared in March and June after operation. Results There was no significant difference in serum CEA and PCT levels between patients of different sexes and ages before operation (P>0.05), but there were significant differences between patients with single lesion and multiple lesions, tumors < 2 cm and ≥2cm, and patients with and without lymph node metastasis (P<0.05). The cutoff value of preoperative serum CEA for predicting MTC lymph node metastasis was 35.75 ng/mL, with sensitivity of 84.61% and specificity of 72.53%. The cutoff value of PCT for predicting MTC lymph node metastasis is 3.65ng/mL, with sensitivity of 86.52% and specificity of 80.77%. Follow-up showed that the serum CEA and PCT levels in patients with recurrence/progression were higher than those in patients with cure at 3 months and 6 months after operation, and the difference was statistically significant (P<0.05). Conclusion Preoperative serum CEA and PCT levels can better reflect the tumor size and the number of lesions in MTC patients, and have a good predictive ability for lymph node metastasis, while postoperative serum CEA and PCT levels can better reflect the progress of the disease.

Key words: carcinoembryonic antigen, procalcitonin, medullary thyroid carcinoma, lymph node metastasis, disease progression