Papillary thyroid microcarcinomas: a comparative study of the characteristics and risk factors at presentation in two cancer registries.

Context: Papillary thyroid microcarcinoma (PTMC) is an indolent neoplasia, often asymptomatic and discovered incidentally. Some PTMCs, however, exhibit a more aggressive behavior, frequently recur, and can even cause cancer-related death. Objective: The aim of this study was to evaluate the prevalence of PTMCs and the associated risk factors at presentation in 2 thyroid cancer registries from areas with different genetic and environmental characteristics. Design and Patients: We conducted a retrospective, observational study of all incident cases of PTMCs recorded over a 5-year period in the Sicilian Regional Registry for Thyroid Cancer (SRRTC) and in the Surveillance Epidemiology and End Results (SEER) US registry. Setting: The study took place at an academic hospital. Results: The incidence of PTMCs was much higher in Sicily (1777 PTMC diagnosed in 2002-2006; age-standardized incidence rate for the world population [ASRw] = 5.8 per 100 000) than in the United States (14 423 PTMC in the period 2004-2008; ASRw = 2.9 per 100 000). Within the SRRTC, a significantly higher incidence was observed in the volcanic area (ASRw = 10.4 vs 4.6 in the rest of Sicily). In Sicily, the female to male ratio was higher, and PTMC patients were younger. In both registries, a significant inverse correlation was observed between age and tumor size. Young patients (<= 45 y) exhibited a higher frequency of nodal metastases. Conclusions: PTMC incidence is twice as high in Sicily compared with the United States, and within Sicily, the incidence is twice as high in the volcanic area. In young patients, PTMCs are larger at presentation and exhibit more risk factors. In both registries, more than 35% of PTMCs exhibited 2 or more risk factors, suggesting that they may require surgery and follow-up similar to that of larger carcinomas. (J Clin Endocrinol Metab 98: 1427-1434, 2013)