Scoring system for predicting recurrences in patients with papillary thyroid microcarcinoma

Context: Papillary thyroid microcarcinomas (PMC) defined as tumors <= 10 mm in diameter (including pT1a and pT3 according to the latest pTNM classification) have good prognosis, although recurrence is possible. Clinicians are interested in using a scoring system for predicting recurrences. Objective: To identify the prognostic factors for recurrence in patients with PMC and to develop a scoring system based on lymph node involvement, multifocality, and sex. To determine the impact of extrathyroidal invasion (ETI) and a threshold value for analyzing multifocality. Methods: Single-center retrospective study of a cohort of 1669 patients with PMC managed from 1960 to 2007. The Kaplan-Meier survival rate and prognostic factors of events were analyzed using logrank tests and uni-and multivariate Cox model-based analyses. A scoring system was proposed. Results: Sixty-eight recurrences were observed. Initial lymph node metastases (P=0.0001), multifocality (P=0.05), and male sex (P=0.01) were significantly associated with recurrence, although there was a period effect (after 1990). PMC size was not a significant variable. Our scoring system allows us to separate patients into three risk groups according to their recurrence-free probability. For PMC Nx patients, total foci size of multifocal tumors >20 mm was significantly associated with recurrence (P<0.0001). Radioiodine (RAI) ablation was associated with better outcome only in PMC with ETI. Conclusion: Our scoring system classifies recurrence risk. In PMC Nx patients, multifocality is important in planning therapeutic strategies. Recurrence probability of pT3 PMC appears lower if RAI ablation is performed.