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

Abstract

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.