A favorable tumor size to define papillary thyroid microcarcinoma: an analysis of 1176 consecutive cases

The optimal treatment strategy for papillary thyroid microcarcinoma (PTMC) has remained controversial. The purpose of this study was to provide a new reference value for PTMC to aid the selection of optimal management for minute lesions.

A pool of 1176 consecutive patients who met the inclusion criteria were ultimately enrolled in this study. The correlation of papillary thyroid carcinoma (PTC) tumor size and lymph node metastasis was analyzed. Receiver operating characteristic curve studies were conducted to identify the reference value by determining the optimal cut-off point of size related to lymph node metastasis. To validate our results, all selected patients were divided into two groups according to the cut-off point and some of the prognostic factors were compared.

A moderate significant correlation was found between the tumor size and the average number of lymph node metastases (r=0.502, P<0.01) and the percentage of lymph node metastasis (r=0.625, P<0.01). The optimal cut-off reference value was 8.5 mm according to the receiver operating characteristic curves. Significant differences were observed for PTC prognostic factors, for example, extrathyroidal extension, multifocality, pathologic (p) N+ stage, occult metastasis in clinical (c) N- stage, radioactive iodine ablation, and recurrence between the two groups.

Due to more aggressive behavior and poorer prognosis in larger tumor size (>8.5 mm), a tumor size ≤8.5 mm in diameter may be favorable to discriminate PTMC from PTC and aid the selection of optimal management.