Significance of multifocality in papillary thyroid carcinoma.

Background: Although multifocality is often observed in papillary thyroid carcinoma (PTC), the associations with clinicopathologic factors and the prognostic value are still controversial. We aimed to identify the risk factors for multifocality and bilaterality, and investigate the significance of multifocality on prognosis in all PTC, papillary thyroid microcarcinoma (PTMC) and non-PTMC.

Methods: Data from 635 patients who underwent lobectomy/total thyroidectomy plus cervical lymph node dissection for PTC were retrospectively analyzed. Clinicopathological factors associated with multifocal PTC and bilateral PTC were investigated by univariate analysis. Multivariate Cox regression analyses was used to identify the clinicopathological prognostic factors for recurrence-free survival.

Results: Multifocal and bilateral PTC were observed in 157 (24.7%) and 99 (15.6%) patients, respectively. The frequency of large diameter (>1.0 cm), extrathyroidal extension (ETE), vascular invasion and central lymph node metastases (CLNM) was higher in multifocal PTC than that of solitary PTC. Moreover, ETE, vascular invasion, CLNM and lateral lymph node metastasis (LLNM) were more frequent in patients with 3 or more tumor foci compared to those with 2 tumor foci and 1 tumor lesion. Bilateral PTC had higher rates of ETE and CLNM. Multifocality was found to be the predictor of recurrence in all PTC, PTMC, and non-PTMC. In addition, the risk of recurrence increased with increasing number of tumor foci in all multifocal PTC patients and multifocal non-PTMC patients.

Conclusion: Although multifocality and bilaterality had more aggressive features in PTC, only multifocality was associated with the increased risk of recurrence. An increase in the number of tumors was associated with an increased risk of ETE, vascular invasion, CLNM and LLNM. The prognostic value of multifocality is particularly significant in non-PTMC patients.