Pre-operative features of non-invasive follicular thyroid neoplasms with papillary-like nuclear features: An analysis of their cytological, Gene Expression Classifier and sonographic findings.

Objective: To investigate the corresponding cytological diagnoses, Gene Expression Classifier (GEC) results and ultrasound features of thyroid nodules diagnosed as non-invasive follicular thyroid neoplasms with papillary-like nuclear features (NIFTP), as well as any coexisting pathology.

Methods: We performed a retrospective review of thyroid nodules histologically diagnosed as NIFTP at our institution between 1st April 2016 and 1st April 2017. The following data points were collected: demographics, nodule size, ultrasound features, cytological diagnosis, GEC results, origin of sample (in-house vs outside hospital) and any additional pathology identified in the resection specimen.

Results: The case cohort included 87 nodules diagnosed as NIFTP (size range: 1-7 cm, mean: 2.5 cm) from 82 patients (age range: 22-82, mean age: 50.4, M:F-1:4.1). Corresponding FNA results were available for 72 nodules (82.8%) and were categorised as follows: benign (n = 5, 6.9%), atypia of unknown significance/follicular lesion of undetermined significance (n = 29, 40.3%), follicular neoplasm/suspicious for follicular neoplasm/follicular neoplasm with oncocytic features (n = 27, 37.5%), suspicious for papillary thyroid carcinoma (n = 6, 8.3%) and malignant (n = 5, 6.9%). GEC results were available for 32 (44.4%) nodules, with the majority of cases classified as suspicious (81.3%). On ultrasound, most of the nodules were predominantly solid (81.8%), vascular (93.8%), non-calcified (86.5%), and either hypoechoic (44.9%) or isoechoic (38.8%). In addition to NIFTP and other benign findings in the background thyroid, 75 separate malignant tumours were identified in 38 (46.3%) patients, many of which were papillary thyroid microcarcinomas (86.5%) with lymph node metastases present in two cases.

Conclusions: The majority of thyroid nodules histologically diagnosed as NIFTP have indeterminate cytology (77.8%) and are classified as suspicious (81.3%) by GEC testing. Taken together, these findings can guide clinicians toward a more conservative therapeutic approach.