Follicular Variant of Papillary Thyroid Carcinoma: Accuracy of FNA Diagnosis and Implications for Patient Management

Abstract

Follicular variant of papillary thyroid carcinoma (FVPTC) creates a continuous diagnostic dilemma among pathologists because of the paucity of nuclear changes of papillary carcinoma and overlapping features with benign and other neoplastic follicular lesions. Current guidelines for the management of thyroid nodules recommend surgery for confirmed PTC, suspicious for PTC, and follicular neoplasm cases, while further immediate diagnostic studies or treatment are not routinely required if the nodule is benign on cytology. This study is designed to determine the accuracy of cytology in the diagnosis of FVPTC, based on the Bethesda classification system, and determine the implications for patient management based on the current recommendation. Based on a retrospective review of cytologic diagnoses between January 2008 and December 2011, thyroid fine needle aspiration (FNA) cytology specimens with subsequent surgical intervention and a final diagnosis of FVPTC were selected. The cytologic diagnoses were compared with the final diagnoses, and the percentage of cases contributing to the final diagnosis of FVPTC was calculated for each diagnostic category. Triage efficiency and diagnostic accuracy were calculated. One hundred and fifty-two cases with histologic confirmation of FVPTC were identified (representing 128 patients-101 female, 27 male). All patients had undergone either lobectomy with completion thyroidectomy or total thyroidectomy. The cytologic diagnosis of "positive for malignancy" accounted for only 27 % of the final histologic diagnosis of FVPTC, while suspicious for carcinoma, follicular neoplasm, follicular lesion of undetermined significance, and benign accounted for 11, 23, 23, and 16 % of the final diagnosis of FVPTC, respectively. Only 18 % of the 55 cases tested were positive for BRAF mutation. The subtle nuclear features of FVPTC pose challenges for an accurate diagnosis. Therefore, a better approach is to triage these cases for surgical intervention and/or further evaluation of the particular nodule. Our triage efficacy for FVPTC was 84 %; however, the diagnostic accuracy of PTC was 38 %. A negative diagnosis on FNA has diagnostic and management implications for up to 16 % of cases because they may have no further immediate diagnostic studies or treatment. BRAF mutation analysis provides minimal effect on diagnostic accuracy.

Noninvasive Follicular Variant of Papillary Thyroid Carcinoma and the Afirma Gene-Expression Classifier

“…Classical type PTCs have more developed nuclear features of PTC compared with FVPTCs. Thus, more classical type PTCs are present in the SUS category than in the AUS/FLUS or SFN categories (19)(20)(21)(22)(23). Our findings are consistent with those reported by Lastra et al who found that of the malignant tumors resected at their institution with a suspicious Afirma result and a preceding AUS/FLUS or SFN diagnosis, 73% were FVPTCs (the FVPTCs were not further subclassified in this study), 14% were classical PTCs, and 14% were FTCs (24).…”

Preoperative Cytologic Diagnosis of Noninvasive Follicular Thyroid Neoplasm with Papillary-Like Nuclear Features: A Prospective Analysis

“…Tumors historically classified as FVPTC do not typically exhibit the full range of cytologic features associated with cPTC and as a result have tended to be classified in the indeterminate categories of the TBSRTC framework, with ''malignant'' aspirates preferentially representing cPTC (17). Architectural alterations of NIFTP/FVPTC also overlap significantly with aspirates in the ''suspicious for a follicular neoplasm'' category (18). Although NIFTP cases are distributed among all TBSRTC categories (6,7), in current practice NIFTP is frequently associated with the ''suspicious for malignancy'' diagnosis (6).…”

Cytological Diagnosis of Follicular Variant of Papillary Thyroid Carcinoma before and after the Bethesda System for Reporting Thyroid Cytopathology

“…FVPTC presents a challenge to pathologists regarding its cytological diagnosis [2,3,6,9,10,11,12]. It has been reported to cause a large proportion of false-negative results in thyroid FNA, with sensitivities ranging from 9 to 37%, and it has been shown that its cytological findings more likely fall into the lower-risk category in comparison to the classical variant [7,9,11,13,14,15].…”