Prognostic significance of tumor multifocality in papillary thyroid carcinoma and its relationship with primary tumor size: a retrospective study of 2,309 consecutive patients.

BACKGROUND: Tumor multifocality is frequently observed in papillary thyroid carcinoma (PTC), but its prognostic value is controversial. We investigated the prognostic significance of multifocality in PTCs larger than 1 cm and papillary thyroid microcarcinomas (PTMC).
METHODS: Medical records and pathologic results of 2,309 patients who received thyroidectomy and lymph node dissection for PTC were retrospectively reviewed. We identified 648 patients who had PTC with a primary tumor exceeding 1 cm, and 1,661 patients with PTMC. In each group, we compared patients with unifocal and multifocal disease. Cox regression analyses of disease persistence and recurrence were performed to identify the prognostic significance of multifocality.
RESULTS: The mean follow-up period was 5.6 years. In the analyses of PTCs larger than 1 cm, the multifocal group included more extensive thyroid surgeries (p = 0.039), radioactive iodine therapies with higher doses (p < 0.001), and significantly higher rates of disease persistence and recurrence (p = 0.001) compared with the unifocal group. In analogous analyses of patients with PTMC, disease persistence and recurrence did not differ significantly between the unifocal and multifocal groups. Cox regression analyses indicated that multifocality was an independent risk factor for disease persistence and recurrence in patients who had PTC with a tumor exceeding 1 cm, but not in patients with PTMC.
CONCLUSION: Tumor multifocality appears to be an important prognostic factor for PTCs larger than 1 cm, but may have little or no prognostic significance for PTMC.