The impact of the non-invasive follicular thyroid neoplasm with papillary-like nuclear feature terminology in the routine diagnosis of thyroid tumours

BACKGROUND: Due to the recent proposal of the non-invasive follicular thyroid neoplasm with papillary-like nuclear feature (NIFTP) category, the authors analyse the state of the art in the challenging diagnosis of follicular thyroid neoplasms in routine practice. METHODS AND RESULTS: A consecutive series of 200 histological diagnoses, with complete cytological correlation, was analysed following the introduction of the NIFTP definition. The study was conducted in a general hospital with a high prevalence of thyroid benign nodules that accounted for approximately 60% of surgically-treated nodules. The significant incidence of the new NIFTP category was 7%. Concurrently, a gradual decrease of the follicular variant of papillary thyroid carcinoma (fvPTC) was observed (3.5%). When evaluating the FNA biopsies within the NIFTP group, despite the systematic evaluation of nuclear crowding, enlargement, irregularities and clearing, the final cytological class was often indeterminate for malignancy (Thy3/III-IV, 71%). At histology, the application of the semiquantitative NIFTP score for the evaluation of the PTC-like nuclear features was able to discriminate benign lesions (score 0/1) from fvPTC (score 2/3). A certain degree of overlapping still persisted between NIFTP and fvPTC (score 2) or between NIFTP and benign lesions (score 1). CONCLUSIONS: In the routine evaluation of FNA biopsies, the presence of subtle and questionable PTC-like nuclear features still remains a controversial aspect of the diagnostic workflow. Given that the NIFTP category was introduced to stratify the low-risk group of thyroid tumours more precisely, pathologists should force themselves to apply the nuclear score rigorously and to classify cases assigned a score of 1 as benign proliferations