Noninvasive Follicular Thyroid Neoplasia With Papillary‐Like Nuclear Characteristics (NIFTP): Clinico‐Pathological Analysis in a Chilean Centre

Introduction Noninvasive follicular thyroid neoplasia with papillary‐like nuclear characteristics (NIFTP) is characterised by an indolent behaviour and was defined in 2016 to avoid overtreatment in differentiated thyroid cancer (DTC). Objectives To report the clinicopathological characteristics and outcomes of patients with NIFTP treated at a Chilean centre between 2016 and 2023. Design Observational retrospective study. Methods Of 1103 patients with thyroid neoplasia treated with surgery, 104 (9.42%) had NIFTP. Clinicopathological variables were recorded, including ultrasound characteristics, fine‐needle aspiration biopsy (FNAB) results, genetic testing when available, type of surgery, tumour size, and follow‐up data. Results Of 104 patients, 85 (81.7%) were female, age of 44 ± 14.2 years and a median tumour size of 1.7 cm (range 0.1–7.1). Eighty‐six (82.7%) had available preoperative staging ultrasound: 1 (1.2%), 39 (45.3%), 38 (44.2%), and 8 (9.3%) were ACR‐TIRADS 2, 3, 4, and 5, respectively. Sixteen (15%) NIFTP were incidental, which were smaller than non‐incidental NIFTP (median 0.4 cm (0.1–2.2) vs. 1.9 cm (0.6–7.1), p < 0.001). Of the 86 FNAB results available, 2 (2.3%), 10 (11.6%), 20 (23.3%), 24 (27.9%), and 30 (34.9%) were Bethesda I, II, III, IV, and V, respectively. Forty‐three patients (41.3%) were treated with lobectomy, 58 (55.8%) with total thyroidectomy (TT), and only 3 (2.9%) with TT and lymph node dissection. In Bethesda II patients, surgery was indicated in cases of nodule growth, showing a larger tumour size than other Bethesda categories (3.0 ± 1.4 vs. 1.8 ± 1.02 cm, p = 0.015). ThyroidPrint® was performed in 12 patients with Bethesda III or IV, resulting suspicious in 11 (92%): of these, 8 (67%) underwent lobectomy. There were no significant differences between lobectomy and TT regarding sex, ACR‐TIRADS, tumour size, or ThyroidPrint® results. Twelve (11.5%) were multifocal and 5 (4.8%) bilateral. Fifty‐two patients (54%) were followed for ≥ 1 year using follow‐up criteria and response to treatment for low‐risk DTC recurrence. Thirty‐four (65%) had excellent response, 15 (28.8%) indeterminate (13 (25%) by biochemical criteria and 2 (3.8%) by ultrasound), 3 (5.7%) incomplete biochemical (2 (3.8%) due to elevated Tg and 1 (1.9%) due to elevated anti‐Tg antibodies), and none with incomplete structural response. There were no differences between lobectomy and TT ± lymph node dissection regarding the type of response. At the end of the follow‐up, there were no deaths, and no new interventions were required due to recurrence. Conclusions In this series, NIFTP showed indolent behaviour and excellent prognosis. Ultrasonographically, 90% presented as ACR‐TIRADS 3 or 4, with less than 10% as ACR‐TIRADS 5. Regarding FNAB, nearly half were indeterminate, one‐third were Bethesda V, and none Bethesda VI. No significant differences in clinical outcomes were found between lobectomy and TT.