Long-term outcome of patients with insular carcinoma of the thyroid: the insular histotype is an independent predictor of poor prognosis

BACKGROUND: Insular thyroid carcinoma was described originally as a tumor with aggressive behavior. However, whether a predominant insular component is an independent factor for poor prognosis is unclear. METHODS: The authors compared the clinical behavior of tumors in three groups of patients with thyroid carcinoma--13 patients with insular thyroid carcinoma, 18 patients with follicular thyroid carcinoma, and 26 patients with papillary thyroid carcinoma--who were selected based on similar tumor size and similar age. Disease free survival and disease specific deaths were assessed in the three groups with a Kaplan-Meier analysis and were compared using the log-rank test. Cox regression analysis was used to evaluate the influence of histotype and other prognostic factors on the occurrence of distant metastases and disease specific death. RESULTS: Patient follow-up ranged from 5.2 months to 190.0 months. At last follow-up, only 1 of 13 patients (7.7%) with insular carcinoma, compared with 8 of 18 patients (44.4%) with follicular carcinoma and 12 of 26 patients (46.1%) with papillary carcinoma, were disease free. The disease specific death rate was 61.5% among patients in the insular carcinoma group compared with 16.7% and 15.4% among patients in the follicular carcinoma group (P = 0.006) and the papillary carcinoma group (P = 0.025), respectively. At multivariate analysis, the insular histotype was the only variable that was related independently to disease specific death (hazard ratio = 4.27; P = 0.005). Distant metastases occurred in 84.6% of patients in the insular carcinoma group compared with 50% and 19.2% of patients in the follicular carcinoma group (P = 0.039) and the papillary carcinoma group (P = 0.0003), respectively. All metastases from patients with insular carcinomas (n = 11 patients) showed radioiodine uptake, but a clinical benefit from this treatment was observed only in 1 patient. CONCLUSIONS: Patients with insular thyroid carcinoma have a poorer outcome compared with patients of similar age who have differentiated types of thyroid carcinoma with tumors of a similar size. Because radioiodine rarely is effective in the treatment of patients with metastatic insular thyroid carcinoma, novel and possible multimodal therapies should be explored for the treatment of patients with these aggressive tumors.