Prognosis and Prognostic Factors for Distant Metastases and Tumor Mortality in Follicular Thyroid Carcinoma

Background: Distant metastases are more common in patients with follicular thyroid carcinoma (FTC) than in patients with papillary thyroid carcinoma, and the outcome is often poorer in patients with distant metastases. In this study, we attempted to identify the risk factors for distant metastases in FTC. Methods: Between 1989 and 1997, 134 patients with FTC underwent initial surgery, and their median follow-up period was 12.5 years. Seventeen patients had widely invasive FTC, and 117 had minimally invasive FTC. Distant metastases were observed in 36 patients (26.9%). Thirteen of these patients had distant metastases at the time of initial surgery (M1), and in the other 23 patients distant metastases were diagnosed with during their follow-up periods. Risk factors for distant metastases and cause-specific survival were analyzed. The factors analyzed were age at the time of initial surgery, sex, primary tumor size, histological findings (invasiveness, extent of vascular, and capsular invasion), and distant metastases at the time of initial surgery. Results: Univariate analysis showed that age and primary tumor size were significant factors related to postoperative distant metastases in the group of 121 patients who did not have distant metastases at the time of initial surgery. When the patients with M1 were included, the cumulative distant metastases-free-survival rate was significantly lower in the group with widely invasive FTC. The cumulative survival rate was significantly higher in the groups of patients with the minimally invasive type, who were under 45 years old, whose primary tumor size was under 4 cm and who did not have distant metastases at the time of the initial surgery. Multivariate analyses showed that tumor size and age were significant risk factors for postoperative distant metastases and that age and the presence of distant metastases at the time of the initial surgery were significant risk factors for poorer cause-specific survival. Conclusion: Age and primary tumor size were significant risk factors for postoperative distant metastases. Based on the findings in this study, we conclude that conservative management is sufficient for younger patients with minimally invasive FTC whose primary tumor is small.