The purpose of this study is to investigate diagnostic and therapeutic strategies that will enable easy differentiation between minimally invasive follicular carcinoma (MIFC) and widely invasive follicular carcinoma (WIFC). We retrospectively reviewed 234 follicular thyroid carcinoma cases to compare the diagnostic and therapeutic characteristics between the minimally and the widely invasive types. Eighty-nine patients were diagnosed with MIFC (mean age, 39.2 ±14.9 years) and 145 were diagnosed with WIFC (mean age, 49.0 ± 17.7 years). Low diagnostic accuracy from preoperative cytology and frozen sections resulted in 60 patients undergoing subtotal thyroidectomies and 57 cases required a second operation for complete thyroidectomy. Patients in the MIFC group were younger, and had small-sized tumors, lower postoperative thyroglobulin levels, lower recurrent rates and lower cancer mortality rates than those in the WIFC group. Diagnostic accuracy from frozen sections in the WIFC group was relatively better. After a mean follow-up period of 9.0±0.4 years, 41 of the 234 (17.5%) patients with follicular thyroid carcinoma had died due to thyroid cancer. All MIFC patients remained disease-free or had a recurrence-free status. In conclusion, both WIFC and MIFC are difficult to diagnose on the basis of preoperative examinations and frozen sections. Patients diagnosed with MIFC had responded positively to the treatment; however, for patients diagnosed with WIFC to become disease-free, early diagnosis and aggressive surgical therapies in combination with (131)I therapy were required.
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