Prophylactic central lymph node dissection in differentiated thyroid cancer.

Conzo et al. [1] describe their experience of treating differentiated thyroid carcinoma in patients who lack clinically evident nodal disease (cN0) with total thyroidectomy, without prophylactic central lymph node dissection, followed by radioactive iodine (RAI). 93.8 % of their 221 patients had AJCC Stage I or II papillary thyroid carcinoma. They report a low locoregional recurrence rate of 3.16 % after almost 10 years as well as low complication rates (0.91 % for both permanent hypoparathyroidism and permanent vocal fold paralysis). The merits of prophylactic lymph node dissection are debated in these patients with early-stage disease, and the authors’ discussion highlights this debate. They note that the current literature lacks conclusive evidence of survival or recurrence benefit, but has established an increase in complication rates (specifically, transient hypocalcemia) associated with prophylactic central nodal dissection compared with total thyroidectomy alone. Based on their results and their scrutiny of this literature, those authors have come to conclude that their treatment paradigm is acceptable and that prophylactic central neck dissection can be avoided [1]. Multiple staging systems for papillary thyroid carcinoma have been developed, many of which do not include cervical nodal metastasis as a factor. However, TNM staging is utilized by the American Thyroid Association in its most recently published guidelines for differentiated thyroid carcinoma. As with other cancers, this system includes clinical staging as well as pathologic staging for nodal metastases. Patients who do not have suspicious cervical lymph nodes by preoperative palpation, preoperative ultrasound, or intraoperative inspection are designated clinically node negative, or cN0. If there are lymph nodes with suspicious characteristics by these evaluations, then patients are considered clinically node positive, or cN1. Pathologic staging is based on microscopic evaluation of nodes in a surgical specimen. Patients without pathologic evidence of nodal disease are staged pN0 and those with disease are designated pN1. The importance of clinical nodal evaluation is evident in the article by Conzo et al. Patients are appropriately classified as cN0 versus cN1, as evidenced by the exclusion of 211 patients who had clinically suspicious lymph node findings by preoperative ultrasound or intraoperative inspection. These cN1 patients underwent therapeutic central nodal dissection rather than prophylactic, and this is a critical distinction. Benefit of central compartment dissection in the setting of clinically positive nodes is widely agreed upon. However, definitive evidence regarding oncologic benefit from dissecting clinically negative nodal basins has yet to be established, and the significance of microscopic nodal disease is widely questioned. A closer look at nodal metastases was recently provided the ATA [2]. In this publication, Randolph et al. note the differences in recurrence risk in node-positive patients based on nodal characteristics. Specifically, cN0 patients who have low volume microscopic central nodal metastases without extranodal extension in neck dissection specimens (making them pN1) still have very low recurrence risk (median 2–4 % which is similar to recurrence risk in cN0 patients in whom nodal dissection is not performed). This is compared with a 22 % recurrence risk in patients who are cN1. Though final TNM nodal staging of these two groups of patients is the same, N1, the marked difference in recurrence between cN0 and cN1 patients highlights the J. A. Goddard (&) D. L. Steward Department of Otolaryngology-Head and Neck Surgery, University of Cincinnati College of Medicine, P.O. Box 670528, 231 Albert Sabin Way, Cincinnati, OH 45267-0528, USA e-mail: julie.goddard@uc.edu