Risk Factors for Nodal Metastasis and Recurrence Among Patients with Papillary Thyroid Microcarcinoma: Differences in Clinical Relevance Between Nonincidental and Incidental Tumors

Papillary microcarcinoma (PMC) is a subgroup of papillary thyroid carcinoma (PTC) measuring 1.0 cm or less in diameter. Herein we focused on the search for risk factors predicting nodal metastasis and recurrence in PMCs, analyzing differences in presentation, treatment, and prognosis between nonincidental and incidental tumors. From January 1998 to May 2007, 149 patients had a diagnosis of PMC in our department. A cross-sectional study of 76 patients with nonincidental and 73 patients with incidental PMC was carried out. Demographic data, diagnostic results, tumor characteristics, risk assessment, surgical treatment, and postoperative and follow up results were evaluated. Cytology detected thyroid cancer and nodal involvement in nonincidental PMC. Mean tumor size was significantly larger in nonincidental PMC (7.5 vs. 4.2 mm), which was commonly found within a normal thyroid gland or Hashimoto's thyroiditis, while incidental PMC was associated with a multinodular goiter. TNM staging system showed a higher cancer stage (IVA) in nonincidental. At multivariate analysis, capsular invasion and a nonincidental diagnosis were the two independent factors significantly affecting nodal metastasis. All patients with nonincidental PMC underwent iodine-131 ablation therapy after surgery compared with 49 patients with incidental. Nodal metastasis at diagnosis was the only factor influencing recurrence which was found in three nonincidental cases: two in the lateral and one in the central neck compartments. Several PMCs presented with risk-free clinical courses. Some nonincidental tumors had a more aggressive behavior and a tendency to recurrence. In these cases, early detection and aggressive treatment are mandatory as for conventional PTC according to risk stratification and cancer stage.