Diagnosis and treatment of small follicular thyroid carcinomas

Background: Follicular thyroid microcarcinomas (mFTCs) of 10 mm or less in size rarely manifest clinically and their clinical significance is controversial. This study assessed their characteristics and incidence, and analysed treatment modalities used for mFTC. Methods: Members of the German Association of Endocrine Surgeons were asked to review patients with mFTC operated on between 1990 and 2005. Results: Data for 90 patients from 26 institutions were reported. Histopathological slides were available for re-evaluation in 35 patients. Most initial diagnoses had to be revised because of incorrect size assessment or incorrect diagnosis (benign adenoma, papillary thyroid carcinoma (PTC), follicular variant of PTC). The diagnosis of mFTC was confirmed in only four patients. As a result of the incorrect histopathological diagnosis, unnecessary completion thyroidectomy and radioiodine ablation were performed in 17 and 20 patients respectively. The incidence of mFTC was calculated to be 0.12 per million population per year. Conclusion: mFTC is exceptionally rare. Such tumours are overdiagnosed, resulting in unnecessary treatment associated with avoidable morbidity. Histopathological re-evaluation by an experienced pathologist is recommended before embarking on further treatments when a diagnosis of mFTC is made.