Diagnostic value of preoperative systemic inflammatory markers and carcinoembryonic antigen in medullary thyroid carcinoma and the risk factors affecting its prognosis.

Background: Medullary thyroid carcinoma (MTC) is a rare malignancy originating from aggressive parafollicular C cells that causes 8-13% of thyroid cancer-related deaths despite its low incidence. Calcitonin and carcinoembryonic antigen (CEA) are considered to be important indicators for the diagnosis of MTC, while serum inflammatory markers have been shown to be valuable in the diagnosis and evaluation of a variety of malignant tumors, but the amount of research literature on MTC is still limited. This article aims to assess the value of serum inflammatory markers, CEA and calcitonin in the differential diagnosis of MTC from papillary thyroid carcinoma (PTC), and to explore the risk factors affecting lateral zone lymph node metastasis of MTC and the clinical features that can be predictive of disease-free survival (DFS). Methods: We retrospectively analyzed 883 patients with PTC and 128 patients with MTC who received care at West China Hospital Sichuan University. The data of clinical characteristics and follow-up results were collected. Results: In our cohort, after performing propensity score matching (PSM), there were 117 patients in the MTC group and 436 in the PTC group. Compared with PTC, MTC patients had higher neutrophil-lymphocyte ratio (NLR) (P=0.008), neutrophil-monocyte-platelet-to-lymphocyte ratio (NMPLR) (P=0.03), and CEA values (P<0.001), and no significant differences were found between the remaining baseline characteristics, with CEA having the largest area under the curve (AUC) in the differential diagnosis of PTC and MTC at 0.898 [95% confidence interval (CI): 0.862-0.934, P<0.001]. Univariate and multivariate logistic regression analyses showed that the occurrence of extrathyroidal extension (ETE) [P=0.002, odds ratio (OR): 4.159, 95% CI: 2.734-5.584], calcitonin level >1,000 pg/mL (P=0.002, OR: 4.785, 95% CI: 3.220-6.350) and CEA level (P=0.04, OR: 1.005, 95% CI: 1.000-1.010) were significantly correlated with lateral zone lymph node metastasis in MTC, while platelet-to-lymphocyte ratio (PLR) was a predictor of DFS. Conclusions: Preoperative blood inflammatory indexes, CEA, and calcitonin level may be able to initially identify MTC and PTC. Meanwhile, ETE, CEA, and calcitonin levels are independent risk factors for lymph node metastasis in the lateral zone of the MTC; therefore, surgeons should consider more carefully planning surgery in conjunction with imaging in patients who have these risk factors at the initial visit.