Follicular variant of papillary thyroid carcinoma: Clinical-pathological characterization and long-term follow-up

PURPOSE: Questions arise concerning the behavior and prognosis of the follicular variant of papillary thyroid carcinoma. PATIENTS AND METHODS: Between 1990 and 2003, 92 patients with follicular variant of papillary carcinoma (group A) were enrolled in a long-term study and compared with control groups of follicular thyroid carcinoma (group B, 40 cases) and pure papillary thyroid carcinoma (group C, 99 subjects). RESULTS: Gender (female/male), age, and follow-up duration (years, mean ± standard error) in groups B, A, and C were 36/4, 43 ± 3, 11 ± 1.1; 79/13, 46 ± 2, 9.5 ± 0.7; and 82/17, 44 ± 1, 10 ± 0.6, respectively. At the time of diagnosis, the rates of extensive extra thyroidal local spread, bilateral lesions, and vascular invasion were higher in group A than in group C. The rate of metastasis tumors was higher in group A than in group C and was comparable in groups A and B. Complete remission was reported in 95% of group B patients, 98% of group C individuals, and in only 77% of group A subjects. Persistent stable lesions and progressive disease rates in groups B, A, and C were 2.5% and 2.5%, 15% and 8%, and 0% and 2%, respectively. The survival rates at the end of the study were 100% in all cohorts, but the cumulative dose of administered radioiodine in group A was higher than in group C and was comparable to that given in group B. Metastases dedifferentiation was observed only in the group A (three patients). DISCUSSION: Follicular variant of papillary thyroid carcinoma may be more aggressive than previously considered and should be clearly distinguished from the two other forms of well-differentiated thyroid carcinoma.