Prophylactic Central Neck Dissection in the Management of Papillary Thyroid Carcinoma; is there a Meaningful Outcome?

Thyroid cancer has the highest increase in incidence rate among all cancers, and this is largely but not full attributed to the increased detection of subclinical papillary carcinomas [1]. As a result, the surgical strategy undertaken in the management of these tumors has been gaining increasing popularity among Endocrinologists and Endocrine Surgeons. Papillary thyroid carcinomas (PTC) are considered favorable prognosis cancers. Most patients have a 5-year overall survival rate well above 90% [2]. Therefore, disease-free survival has replaced overall survival as the main outcome of interest when effective initial management of these tumors is evaluated. Given the high incidence of occult nodal metastasis in PTC, advocating prophylactic central compartment neck dissection (pCCND) for the initial management of these tumors is, in theory, the ideal thing to do. Nevertheless, the role of pCCND in the management of PTC remains controversial regarding its benefits and risks [3-6].


Introduction
Thyroid cancer has the highest increase in incidence rate among all cancers, and this is largely but not full attributed to the increased detection of subclinical papillary carcinomas [1]. As a result, the surgical strategy undertaken in the management of these tumors has been gaining increasing popularity among Endocrinologists and Endocrine Surgeons. Papillary thyroid carcinomas (PTC) are considered favorable prognosis cancers. Most patients have a 5-year overall survival rate well above 90% [2]. Therefore, disease-free survival has replaced overall survival as the main outcome of interest when effective initial management of these tumors is evaluated. Given the high incidence of occult nodal metastasis in PTC, advocating prophylactic central compartment neck dissection (pCCND) for the initial management of these tumors is, in theory, the ideal thing to do. Nevertheless, the role of pCCND in the management of PTC remains controversial regarding its benefits and risks [3-6].
Prophylactic neck dissection is defined as neck dissection in the absence of clinical evidence of nodal involvement whether on preoperative examination and imaging studies or during intraoperative evaluation. It is synonymous with elective/routine dissection [7].
Essential to any assessment of the role of pCCND is to verify its oncologic rationale and whether its benefit outweighs its potential morbidity. Proposed potential benefits of pCCND include: eliminating a potential source of recurrence subsequently avoiding potential morbidity of revision surgery, increasing the accuracy of disease staging for radioactive iodine (RAI) dosing and long-term follow up, and improved accuracy of thyroglobulin surveillance [6]. While occult node positivity is quite common in PTC (even in subcentimetric cancers), it rarely demonstrates prognostic parameters of recurrence and/or a possibly worse diseasespecific survival. Occult metastases usually tend to be small in size and number, with no extranodal extension, and a median risk of recurrence of only 2% [8]. Moreover, the comparability in oncologic outcome between those who undergo pCCND and those who do not is a testimony to the indolent biologic behavior of subclinical nodal disease [9][10][11][12][13][14]. Further proof of the clinical stability of occult nodal disease, is the rare progression to locoregional recurrence among untreated patients [15] or those who did not receive RAI adjuvant therapy [16]. A recent meta-analysis demonstrated that the presence of occult central nodal metastasis was not a significant predictor of recurrence nor did pCCND improve local control [17]. Reoperation for recurrent disease in the central neck, despite being uncommon, is challenging.

Open Access Journal of Surgery
However, in experienced hands the safety of CCND as a secondary operation was comparable to it as a primary one [18,19].
One of the arguments for the use of pCCND is that it influences the usage of RAI through identifying the true nodal status of patients. Accordingly patients may be stratified to receive higher doses of RAI [13] or spared empiric postoperative RAI therapy [20]. The American joint committee on cancer (AJCC) tumor, nodal disease and distant metastasis (TNM) staging system considers nodal metastasis a prognostic factor for patients above the age of 45 years [21]. However, it does not differentiate between microscopic and macroscopic metastases that have different implications on outcome. Therefore, microscopic upstaging may lead to potentially unnecessary or additional treatments and reevaluations that are not devoid of adverse consequences [22]. On the other hand, giving empiric postoperative RAI based on the assumption of node positivity does not seem to be appropriate especially that the clinical stability of occult metastases in untreated patients or those who did not receive postoperative RAI has been demonstrated [15,16].
Performing pCCND is in theory a step forward towards achieving athyroglobulinemia and improving surveillance accuracy. Nevertheless, the literature has been inconsistent in demonstrating this [5,13,23]. Furthermore, factors other than the normalization of serum thyroglobulin levels play a more important role in modifying follow-up management [2]. As far as morbidity of pCCND is concerned it has been demonstrated that studies comparing total thyroidectomy alone to that with pCCND, show a significant increase in transient hypoparathyroidism and a trend towards increased permanent hypoparathyroidism and RLN injury with the latter [2]. Therefore, it seems fair to say that since pCCND does not have a favorable prognostic impact (in terms of both disease-specific and disease-free survival), and is associated with an increased risk of postoperative morbidity avoiding the procedure in clinically node negative patients would translate into preservation of their quality of life following surgery. This in turn is considered an extremely meaningful outcome particularly in oncologic patients, and has been demonstrated in the first prospective randomized controlled trial on the role of pCCND in the management of PTC in literature conducted at the author's centre.
As the vast majority of PTCs are associated with nodal micrometastasis studies focusing on clinical predictors of recurrence rather than nodal metastasis occurrence are required to guide the selection of potential subgroups of patients in which pCCND could be recommended. In conclusion, the low recurrence rate in the central neck combined with the potential for increased morbidity from pCCND or the need for RAI or its higher doses as a result of microscopic upstaging of tumors outweighs the potential benefits of routinely performing the procedure. Therefore, thyroidectomy without pCCND seems to be appropriate for patients with PTC in the absence of clinically apparent metastatic nodes.

Disclosure
The author has no financial ties or conflicts of interest to disclose.