Follicular thyroid carcinoma (FTC) is the second most common malignancy of the thyroid after papillary thyroid carcinoma, constituting about 10% of all thyroid malignancies. The objective of the current investigation was to determine whether there was a direct relationship between the histologic degree of invasion, tumor recurrence, and patient survival.

We retrospectively reviewed the records of 55 patients with a histologic diagnosis of pure follicular carcinoma of the thyroid who were treated from 1990 to 2003 at the Presbyterian Medical Center in Jeonju, Korea. Their mean follow-up period was 8.4 years (range, 1~15 years). The following criteria were used to histologically define malignant follicular neoplasms: 1) minimally invasive, tumor invasion through the entire thickness of the tumor capsule; 2) moderately invasive, tumor with angioinvasion (with or without capsular invasion); and 3) widely invasive, broad area or areas of transcapsular invasion of thyroid and extrathyroid tissue.

Among 33 patients with capsular invasion only, 2 patients (6%) developed recurrent disease. Of the 16 patients who had angioinvasion with or without capsular invasion, 4 patients (25%) developed recurrent disease. Among 6 patients who had widely invasive FTC, 5 patients (83%) developed recurrent disease, and 2 of those 6 patients (33%) with widely invasive FTC died of the disease. Patients who had widely invasive FTC had greater recurrence rates than patients who had a capsular or angioinvasion (P<0.001). The overall death rate for patients with widely invasive FTC was 33%.

This study shows that patients with widely invasive FTC had greater recurrence rates and poorer survival than patients who had capsular or angioinvasion; this difference was statistically significant. The authors conclude that patients who had widely invasive FTC need close follow-up and active treatment.