Total surface area is useful for differentiating between aggressive and favorable multifocal papillary thyroid carcinomas

Purpose: The purpose of the present study was to identify more useful parameters for predicting behaviors of multifocal papillary thyroid carcinoma (PTC). Materials and Methods: We investigated dominant tumor diameter (TD), total tumor diameter (TTD), and total surface area (TSA) in tumors from 588 patients and evaluated their usefulness as parameters for assessment of tumor behaviors in multifocal PTCs. Results: In 588 PTCs, tumor multifocality was found in 179 PTCs (30.4%). Multifocal tumors were significantly associated with extrathyroidal extension, lymph node metastasis, and higher tumor stage grouping (p<0.001, p<0.001, and p<0.001, respectively). The rates of nodal metastasis increased with greater TSA and TTD in PTCs. Multifocal papillary thyroid microcarcinomas (mPMCs) with TSA >3.14 cm² had higher rates of nodal metastasis than mPMCs with TSA ≤3.14 cm² (p=0.038); however, there was no significant difference between mPMCs with TTD >1.0 cm and with TTD ≤1.0 cm (p=0.325). In addition, nodal metastasis was more frequent in mPMCs with TSA >3.14 cm² than in unifocal papillary thyroid microcarcinomas (uPMCs) (TD ≤1.0 cm) (p=0.002), but not overt unifocal PTCs (TD >1.0 cm) (p=0.244). Conclusion: Our results suggest that mPMCs with TSA >3.14 cm² show more aggressive behavior than uPMCs and mPMCs with TSA ≤3.14 cm². TSA could be useful in distinguishing aggressive mPMCs from favorable cases.