The Prognostic Value of Tumor Multifocality in Clinical Outcomes of Papillary Thyroid Cancer.

Context: Multifocality is often treated as a risk factor for papillary thyroid cancer (PTC), prompting aggressive treatments, but its prognostic value remains unestablished. Objective: To investigate the role of tumor multifocality in clinical outcomes of PTC. Methods: Multicenter study of the relationship between multifocality and clinical outcomes of PTC in 2638 patients (623 men and 2015 women) with median [interquartile range (IQR)] age of 46 (35 to 58) years and median (IQR) follow-up time of 58 (26 to 107) months at 11 medical centers in six countries. Surveillance, Epidemiology and End Results (SEER) data were used for validation. Results: Disease recurrence in multifocal and unifocal PTC was 198 of 1000 (19.8%) and 221 of 1624 (13.6%) (P < 0.001), with a hazard ratio of 1.55 [95% confidence interval (CI), 1.28 to 1.88], which became insignificant at 1.13 (95% CI, 0.93 to 1.37) on multivariate adjustment. Similar results were obtained in PTC variants: conventional PTC, follicular-variant PTC, tall-cell PTC, and papillary thyroid microcarcinoma. There was no association between multifocality and mortality in any of these PTC settings, whereas there was a strong association between classic risk factors and cancer recurrence or mortality, which remained significant after multivariate adjustment. In 1423 patients with intrathyroidal PTC, disease recurrence was 20 of 455 (4.4%) and 41 of 967 (4.2%) (P = 0.892) and mortality was 0 of 455 (0.0%) and 3 of 967 (0.3%) (P = 0.556) in multifocal and unifocal PTC, respectively. The results were reproduced in 89,680 patients with PTC in the SEER database. Conclusions: Tumor multifocality has no independent risk prognostic value in clinical outcomes of PTC; its indiscriminate use as an independent risk factor, prompting overtreatments of patients, should be avoided.