Revised criteria for diagnosis of NIFTP reveals a better correlation with tumor biological behavior

Abstract

The recent reclassification of a follicular variant of papillary thyroid carcinoma (FVPTC), subset as noninvasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP), aims to avoid overtreatment of patients with an indole nt lesion. The diagnosis of NIFTP has recently been revisited using more rigid criteria. Th is study presents histological and molecular findings and a long clinical follow-up of 94 FVPTC , 40 cases of follicular adenoma (FTA) and 22 cases of follicular carcinoma (FTC) that w ere classified before the advent of the NIFTP reclassification. All slides were reviewed u sing these rigid criteria and analysis of numerous sections of paraffin blocks and reclassified as 7 NIFTPs, 2 EFVPTCs, 29 infiltrative FVPTC (IFVPTCs), 57 invasive EFVPTC (I-EFVPTCs), 39 FTAs and 22 FTCs. Remarkably, EFVPTC and NIFTP patients were all free of disease at the end of follow-up and showed no BRAF mutation. Only one NIFTP sample harbored mut ations, an NRAS Q61R. PAX8/PPARG fusion was found in I-EFVPTCs and FTC. Although additional stu dies are needed to identify a specific molecular profile to aid in the diagnosis of lesions with borderline morphological characteristics, we confirmed that the BRAF V600E mutation is an important tool to exclude the diagnosis of NIFTP. We also show that rigorous histopathological criteria should be strongly followed to avoid missing lesions in which more aggressive behavior is present, mainly via the analysis of capsule or vascular invasion and the presence of papillary structures.

Keywords

• papillary thyroid carcinoma
• niftp
• braf v600e
• ras
• pax8-pparg