Papillary thyroid carcinoma micro-deposits in cervical lymph nodes without intra-thyroid malignancy: A comment in consideration of the latest American Thyroid Association guidelines.

Differentiated thyroid cancer (DTC) represents the vast majority of all thyroid cancers, with the papillary variant being the most common. According to the previous 2009 American Thyroid Association (ATA) guidelines, papillary thyroid microcarcinoma (PTMC; ≤1 cm in diameter) exhibiting cervical lymph node metastasis corresponded to an intermediate-risk group for recurrence or metastasis. However, the latest 2015 ATA guidelines advocate that a patient with PTMC is low-risk if there are ≤5 regional node micrometastases. This means that therapeutic radioactive iodine (RAI) is not required. The current study reports a rare case of a patient who underwent total thyroidectomy due to multi-nodular goiter where the pathologic specimen exhibited two PTMC foci in regional lymph nodes, but no primary cancer was identified in the thyroid despite thorough examination of the thyroid parenchyma. The etiology of such results is unknown and it was hypothesized that it may be the consequence of insufficient pathologic examination or due to the regression of a primary PTMC in the thyroid. Moreover, the risk-stratification of cases with intra-lymph node PTMC without any evidence of primary cancer in the thyroid is not considered in the ATA recommendations. The aim of the current report was to elucidate the risk-stratification of this rare occurrence and to reconsider the possible etiologies. By extrapolating the latest ATA recommendations concerning a patient with a known primary PTMC and ≤5 metastatic micro-foci (thus the only difference between cases being the absence of a primary tumor), it was concluded that the patient should be considered low-risk. As a consequence, RAI therapy should be deemed as unnecessary despite the presence of lymph node microfoci. Moreover, it was proposed that cervical lymph node PTMC with no evidence of a primary tumor in the thyroid could be the consequence of normal thyroid tissue micro-deposit progression to cancer within the lymph node, which is a rare benign entity.