Endocrine Abstracts

Introduction: The Bethesda System for Reporting Thyroid Cytopathology is the standard for interpreting fine-needle aspiration (FNA) and created a new diagnostic category (III): ‘atypia of undetermined significance/follicular lesion of undetermined significance’ (AUS/FLUS). The risk of malignancy for this category has been ascribed of 5–15% but the real malignancy rate remains unclear and plays a key role to define appropriate management.

Objective: To determine malignancy rate in AUS/FLUS cytologies.

Methods: A total of 126 consecutive patients with AUS/FLUS cytology were retrospectively identified. Results of follow-up, repeat biopsy or surgical pathology were evaluated. Data are presented as frequencies. For comparison we performed Student’s t-test (statistically significance <0.05).

Results: Among 126 patients, 19.0% (24/126) underwent immediate surgery and 50.0% (63/126) repeated FNA. Of patients immediately submitted to surgery, just one was found to have a papillary microcarcinoma inserted into the index lesion, the remaining suspicious nodules being benign. We found five incidental papillary carcinomas (4 <1 cm). Repeat FNA cytology was unsatisfactory/non-diagnostic in 22.2% (14/63), benign in 17.5% (11/63), AUS/FLUS in 49.2% (31/63), suspicious for malignancy in 9.5% (6/63), and malignant in 1.6% (1/63). Of nodules with two consecutive AUS/FLUS cytologies that were resected (21/31), 23.8% (5/21) were malignant and in one case the lesion couldn’t be determined as benign/malignant. We found no statistical significance regarding nodule size and probability of malignancy of the suspicious nodule (31.7 mm vs 23.0 mm, P=0.145). Overall, 57 patients underwent surgery to remove the index lesion, yielding a malignancy rate of 19.3% (11/57), as one case couldn’t be classified by histology. Incidental cancers were found in 21.0% (12/57).

Conclusions: Repeating biopsy allows a significant proportion of AUS/FLUS patients to avoid surgery. In our series, nodules with two AUS/FLUS cytologies harbour a malignancy rate of 23.8%. Incidental papillary carcinomas cancers are frequent (21.0%), in accordance with its high prevalence in general population.