Occult lymph node metastases increase locoregional recurrence in differentiated thyroid carcinoma.

Objectives: The impact of occult lymph node metastasis (OLNM) on locoregional recurrence (LRR) and survival in patients with NO differentiated thyroid carcinoma is unclear, because no large study has been carried out. A retrospective study was conducted in our department to assess the influence of OLNM.

Methods: We included 201 patients treated by prophylactic neck dissection for NO differentiated thyroid carcinoma between 1974 and 2006. The incidence of OLNM and predictive factors for recurrence and survival were assessed.

Results: The incidence of OLNM was 20%. Necks were involved at levels VI, III, II, IV, V, and I, in decreasing order of frequency. After a mean follow-up of 9 years, the rate of LRR was 8.9% and the rate of distant metastasis was 3.4%. An age of greater than 55 years and the presence of OLNM were predictive factors for LRR. An age of greater than 55 years and the presence of LRR were predictive factors for distant metastasis. The presence of distant metastasis was the only factor that significantly and independently influenced the disease-specific survival.

Conclusions: We found that OLNM occurred in only 20% of NO patients. The presence and especially the number of OLNMs on neck dissection were major risk factors for LRR in this study, but did not affect the disease-specific survival.