Background: The need for prophylactic lateral neck dissection (LND) in medullary thyroid carcinoma (MTC) patients without clinically evident lateral lymph node (LN) metastasis remains controversial, particularly in those with elevated preoperative calcitonin levels. This study investigated the prognostic impact of prophylactic LND in MTC patients with preoperative calcitonin levels >200 pg/mL, but without clinically suspicious lateral LNs.

Materials and methods: This multicenter retrospective cohort study included 103 patients with MTC treated between January 1980 and December 2022 at two tertiary hospitals in Seoul, South Korea. Patients had preoperative calcitonin levels above 200 pg/mL and no clinical evidence of lateral LN metastasis. They were divided into two groups based on whether LND was performed, and their long-term oncological outcomes were compared.

Results: The median follow-up duration was 90 months. The LND group had significantly larger tumors and higher preoperative calcitonin levels. Although the biochemical cure rate was higher in the LND group than in the No LND group (95.2% vs. 82.5%), this difference was not statistically significant (P = 0.074). No significant differences were observed between the groups in biochemical recurrence, structural recurrence, overall survival, or disease-specific survival. Subgroup analyses based on preoperative calcitonin levels showed comparable results.

Conclusion: Prophylactic LND did not significantly impact long-term oncologic outcomes in MTC patients without clinically evident lateral LN metastasis, even among those with elevated preoperative calcitonin levels above 200 pg/mL. Although prophylactic LND was associated with higher biochemical cure rates, this did not translate into reduced recurrence rates or improved survival. Routine prophylactic LND may not be necessary, and the decision to perform it should be carefully individualized based on patient-specific factors.