The Flip Side of NIFTP: an Increase in Rates of Unfavorable Histologic Parameters in the Remainder of Papillary Thyroid Carcinomas

Abstract

The term noninvasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP) was recently proposed to replace noninvasive follicular variant of papillary thyroid carcinoma (FVPTC) both to promote more conservative management of these tumors and spare patients the psychological burden of a cancer diagnosis. This reclassification will lower the incidence of papillary thyroid carcinoma (PTC). In addition, it could result in an increase in the rates of unfavorable histologic prognosticators for PTC overall because NIFTPs had previously accounted for many of the PTCs without these features. Our aim was to evaluate the potential impact of the reclassification of NIFTP on the rates of extrathyroidal extension, lymphovascular invasion, and lymph node metastases in PTC. We identified all PTCs clinically over 1 cm diagnosed on surgical resection between August 2010 and August 2012. The histopathologic characteristics, including PTC subtype, tumor size, presence of extrathyroidal extension and lymphovascular invasion, and surgical margin and lymph node status were all recorded. Based on these parameters, cases were classified according to the American Thyroid Association (ATA) risk stratification system for structural disease recurrence. Tumor slides for cases initially diagnosed as FVPTC were reviewed to identify tumors that would now be classified as NIFTPs. Our cohort included 348 cases of PTC, of which 94 (27%) would now be classified as NIFTPs. After excluding NIFTPs from the PTC category, there were increased rates of extrathyroidal extension (26% up from 19%, p = 0.046), lymphovascular invasion (37% up from 27%, p = 0.0099), and lymph node metastases (26% up from 19%, p = 0.045) among the remaining PTCs. Based on these changes in histologic features, 10% fewer cases were defined as ATA low risk (62% down from 72%, p = 0.0081). Our results indicate that the downgrading of some carcinomas to NIFTP will increase the rates of higher risk histologic parameters in the remaining PTCs by statistically significant margins. Although the overall survival for PTC is very high and would likely not be changed significantly by the introduction of NIFTP, additional studies evaluating the impact of the NIFTP shift are warranted.

The influence of the noninvasive follicular thyroid neoplasm with papillary‐like nuclear features (NIFTP) resection diagnosis on the false‐positive thyroid cytology rate relates to quality assurance thresholds and the application of NIFTP criteria

“…Specifically, features such as >1% true papillae formation, psammoma bodies, and the focal presence of other variants of PTC (eg, >30% solid, trabecular, or insular growth pattern) may have been overlooked in cases previously diagnosed as noninvasive encapsulated FVPTC before NIFTP inception. A recent study by Wong et al has shown that the delineation of NIFTP criteria has increased the rates of unfavorable histologic parameters in PTCs that do not qualify as NIFTP . Moreover, a few implicit criteria regarding NIFTP are worth mentioning.…”

“…A recent study by Wong et al has shown that the delineation of NIFTP criteria has increased the rates of unfavorable histologic parameters in PTCs that do not qualify as NIFTP. 24 Moreover, a few implicit criteria regarding NIFTP are worth mentioning. First, oncocytic neoplasms were not included in the original NIFTP report and therefore were not part of the current study.…”

Noninvasive follicular thyroid neoplasm with papillary-like nuclear features: a problematic entity

“…The predictions, which were based on retrospective data from four institutions (three Italian and one American), resulted in a calculated rate of NIFTP of 18.6% among all PTC cases (4). After more than 3 years from the introduction of the new nomenclature, it appears that the initial calculations were overestimated (8,9,10,11,12,13,14,15,16,17,18,19,20,21).…”

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

“…Additionally, in our study lymph node metastases were present in only two cases; one case had a PTC with tall cell features and both cases had multifocal microcarcinomas. Although examination of the negative histological features associated with PTCs was beyond the scope of our study, Wong et al noted that in reclassifying NIFTPs as benign neoplasms, the rates of unfavourable parameters such as extrathyroidal extension, lymphovascular invasion and lymph node metastases increased in the other subtypes of PTCs. More studies with long‐term follow‐up will be needed to fully characterise the prognostic implications of this diagnostic paradigm shift on other PTCs.…”