Follicular thyroid carcinoma: histology and prognosis.

BACKGROUND: Follicular thyroid carcinoma (FTC) is the second most common thyroid malignancy after papillary thyroid carcinoma. The authors studied the clinical course of 132 patients with FTC to determine whether there was a direct relation between the histologic degree of invasion, tumor recurrence, and patient survival.

METHODS: The 132 patients in the study population underwent 182 thyroid carcinoma-related operations, and their mean follow-up was 7.5 years (median:,6 years; range, 0-39 years). The following criteria were used to 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 extrathyroidal tissue. Forty-five of 119 patients (37.8%) presented with minimally invasive FTC (capsular invasion only), 50 patients (42%) presented with moderately invasive FTC (angioinvasion with or without capsular invasion), and 24 patients (20%) presented with widely invasive FTC. At presentation, 12 patients (9%) had distant metastases, and 8 patients (6%) had lymph node metastases.

RESULTS: Excluding 12 patients who presented with distant metastases, 21 patients (16%) developed recurrent metastases 6 months after their initial treatment. Among 45 patients with capsular invasion only, 6 patients (13%) developed recurrent or persistent disease, and 5 patients (11%) died. Of the 50 patients who had angioinvasion with or without capsular invasion, 10 patients (20%) developed recurrent or persistent disease, and 7 patients (14%) died. Patients who had angioinvasion with or without capsular invasion had a less favorable prognosis compared with patients who had capsular invasion only (P < 0.0001). Among patients who had widely invasive FTC, 9 of 24 patients (38%) developed recurrent disease, and 8 patients (33%) died; in addition, 7 of the other 24 patients (29%) had persistent disease and died. The overall death rate for patients with widely invasive FTC was 62%. Patients with persistent disease had a poorer prognosis compared with patients who had recurrent disease (P < 0.0001). Twenty-eight patients (21%) in the entire group died of FTC.

CONCLUSIONS: In the current retrospective investigation, the authors demonstrate that patients with minimally invasive FTC (capsular invasion only) had a slightly better survival rate at 5 years (98%) compared with patients who had angioinvasion with or without capsular invasion (80%) and had better survival compared with patients who had widely invasive FTC (38%). Other (but not all) reports in the literature support the findings that FTC with angioinvasion is more aggressive than FTC with only capsular invasion yet is less aggressive than widely invasive FTC. The authors conclude that FTC no longer should be classified as either minimally invasive or widely invasive; rather, they recommend classifying FTC as minimally invasive, moderately invasive, or widely invasive, because prognosis varies according to these groupings.