Suggesting the cytologic diagnosis of noninvasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP): A retrospective analysis of atypical and suspicious nodules.

BACKGROUND

The term "noninvasive follicular thyroid neoplasm with papillary-like nuclear features" (NIFTP) has replaced a subset of follicular variant of papillary thyroid carcinoma due to the indolent behavior of such tumors. NIFTPs are most often classified in an "indeterminate" diagnostic category. In the current study, the authors sought to identify cytologic features helpful in distinguishing NIFTP from other entities in these categories, particularly benign nodules.

METHODS

The authors retrospectively evaluated a consecutive cohort of 130 thyroid fine-needle aspiration (FNA) specimens with an indeterminate diagnosis and available histopathologic follow-up. All FNA specimens were evaluated using the ThinPrep method. Each FNA was blindly reviewed by 2 board-certified cytopathologists, who assessed overall cellularity; architectural parameters; and nuclear features, including nuclear pallor and fine chromatin, distinct nucleoli, and irregular nuclear membranes. Each case received a score of 0 to 3, based on the presence or absence of these 3 nuclear features.

RESULTS

Nuclear but not architectural features appeared to distinguish NIFTP from benign nodules. Ninety-one percent of the NIFTPs (32 of 35 NIFTPs) received a score of ≥2, compared with 35% of benign nodules (23 of 66 benign nodules) (P<.0001). In contrast, NIFTP could not be differentiated from the invasive/infiltrative follicular variant of papillary thyroid carcinoma using these criteria (P = 1.000). Nuclear scoring was found to be especially useful in atypia of undetermined significance/follicular lesion of undetermined significance (AUS); a score ≥2 enriched for NIFTP (39% vs 3% of AUS cases with a score <2), whereas a score <2 was more likely benign (85% vs 50% of AUS cases with a score ≥2).

CONCLUSIONS

In indeterminate FNA specimens, the distinction of a possible NIFTP from a benign thyroid nodule can be suggested using a simple nuclear scoring system that is most valuable in AUS aspirates. Cancer Cytopathol 2018;126:86-93. © 2017 American Cancer Society.