Can We Predict the Lateral Compartment Lymph Node Involvement in RET-Negative Patients with Medullary Thyroid Carcinoma?

Background: Lateral lymph node dissection (LND) in the absence of macroscopic nodal metastasis remains controversial in sporadic medullary thyroid carcinoma (MTC). Objectives: The aims of our study were to determine the risk of lateral lymph node (LN) metastases with a focus on lateral contralateral N1, and to define a risk-adapted surgical treatment for these patients. Methods: All patients who underwent surgery from 1980 to 2012 for previously untreated RET-negative MTC were reviewed. We focused on the lateral compartments of LN metastases and identified three groups: no lateral LN metastases, ipsilateral lateral (ILL)–LN metastases with no contralateral LN involvement, and contralateral lateral (CLL)–LN metastases. Results: Overall, 131 patients underwent surgery for RET-negative MTC. A total thyroidectomy with LND was performed in 112 patients (85 %), including 97 patients who had an ILL–LND and 92 patients who had a CLL–LND. Lateral LN metastases (N1) occurred in 40 patients (37 %): 31 patients (32 %) had ILL–LN metastases with no contralateral LN involvement, and 9 patients (10 %) had CLL–LN metastases. The preoperative cut-offs for LN metastases in the ILL compartment were very low, with a smallest tumor size of 5 mm, and lowest serum calcitonin level of 38 pg/ml. Disease-free survival rates decreased from 92 % for patients with no lateral LN metastases to 41 % for patients with ILL–LN metastases and 0 % for patients with CLL–LN metastases. Conclusions: ILL–LND should be performed in every patient and only a minority of MTC patients with small micro-MTC, and low serum calcitonin levels should not have a CLL–LND.