Clinical importance of follicular lesion of undetermined significance (diagnostic category III according to Bethesda System) diagnosed from Fine-Needle Aspiration Biopsy.

Introduction: Follicular Lesion of Undetermined Significance (FLUS) belongs to the most controversial category of the Bethesda System. The aim of the study was to specify the risk of malignancy in patients with FLUS diagnosis in the material from the Institute of Oncology in Gliwice. This is the first Polish study specifying the risk of malignant neoplasm presence when Fine-Needle Aspiration Biopsy (FNAB) results in a report of diagnostic category III (DC III).

Material And Methods: Three hundred and ninety-five primary DC III diagnoses from FNABs of the thyroid gland performed from 2010 to 2015 were analysed. Correspondence of DC III with diagnoses from repeated FNABs and histopathology reports was evaluated.

Results: From 395 DC III patients, 27 were treated surgically for clinical indications, receiving six diagnoses of cancer. Repeat FNAB was performed in 180 cases, and primary diagnosis was confirmed in 41 cases. In the second FNAB there was one diagnosis of "Papillary Thyroid Carcinoma" and one "Suspicious for Papillary Thyroid Carcinoma". From eight patients treated surgically in these series prior cytological cancer diagnosis was confirmed in two cases. Forty-six patients were subjected to third and subsequent FNABs; in one case the diagnosis was "Suspicious for Malignancy". In the analysed material the risk of cancer in patients with FLUS is 2.78%. Taking into account all 56 subsequent FNABs in which the primary diagnosis was confirmed, the risk decreases to 2.43%.

Conclusions: The diagnosis of FLUS in the absence of clinical indications is not a basis for surgical treatment.