Endocrine Abstracts

Introduction: The Bethesda System for Reporting Thyroid Cytopathology (TBSRT) allows the correlation between six individual diagnostic categories with the risk of malignancy, and offers a standardized management algorithm for each category. Atypia of undetermined significance (AUS) and follicular neoplasm categories are considered indeterminate categories, with varying malignancy rates and subtypes.

Aim: To establish the malignancy rate and subtype of cancer in thyroid nodules with indeterminate cytology results and to observe their clinical evolution.

Materials and Methods: We retrieved from our endocrinology center database all fine-needle aspiration (FNA) procedures performed by a single endocrinologist between February 2018 and April 2023. We excluded the first 500 procedures, which represented the learning curve, and all parathyroid and lymph node FNA procedures.

Results: There were 2465 nodules. Of the 51 (2.06%) patients with AUS, 15 (29.41%) patients had an available pathology report: 11 (73.33%) patients with follicular adenoma and 4 (26.66%) patients with thyroid carcinoma - 1 classic papillary thyroid carcinoma (PTC), 2 diffuse sclerosing PTC, 1 medullary thyroid carcinoma (MTC). Of the 100 (4.05%) patients with follicular neoplasm, 57 (57%) had an available pathology report: 31 (54.38%) patients with follicular adenoma and 26 (45.61%) patients with thyroid carcinoma - 21 patients with PTC (9 classic, 5 follicular, 2 tall cell, 2 diffuse sclerosing, 1 solid/trabecular, 1 NIFTP, 1 oncocytic), 4 with follicular neoplasm and 1 with poorly differentiated thyroid carcinoma. Twenty (66.66%) patients with carcinoma underwent radioiodine therapy, 11 (36.66%) had a suppressed thyroglobulin at the last follow-up, 4 (13.33%) had a persistent/recurrent local disease, 4 (13.33%) had metastatic disease and 10 (34.48%) were lost to follow up. The patient with MTC had a negative MEN2A screeing, a negative RET mutation and an increasing serum calcitonin value at the last follow up. None of the patients have had a thyroid carcinoma related death.

Conclusions: Although the majority of operated nodules with indeterminate cytology results are benign (58.33%), these results reported in our centre are lower than literature data. The most common type of carcinoma in these patients was classic PTC (33.33%). The clinical evolution of these patients varies widely according to malignancy subtype.