Distant metastases from pathologically proven benign follicular nodules of the thyroid: clinicopathological features and predictors of long-term survival

Distant metastases are rarely observed in patients with initial pathologically proven benign follicular nodules of the thyroid. This study aimed to evaluate the clinicopathological features and independent variables associated with survival in such patients with distant metastases. In total, 10,992 consecutive differentiated thyroid cancer (DTC) patients treated with 131I after total or near-total thyroidectomy from 2000 to 2018 were retrospectively reviewed. Thirty-nine patients with initial pathologically proven benign follicular nodules of the thyroid were enrolled. Among them, 26 were pathologically diagnosed as thyroid adenoma, 8 as benign nodular goiter, 4 as thyroid adenoma combined with benign nodular goiter, and 1 as normal thyroid tissue. Of 26 patients with the initial pathological slides obtained, eight cases were rediagnosed as minimally invasive thyroid carcinoma (MI-FTC), 10 as follicular tumor of uncertain malignant potential (FT-UMP), and five as well-differentiated tumor of UMP (WDT-UMP). Monitoring of thyroglobulin (Tg) changes after initial thyroidectomy and preablation-stimulated Tg (psTg) level were significantly associated with 5-year OS rate (P = 0.007 and P = 0.005, respectively). The presence of radioactive-refractory DTC (RR-DTC), monitoring of Tg changes after initial thyroidectomy, and psTg level had significant effects on 10-year OS rate (P = 0.002, P