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. 2022 Nov;32(11):1353-1361.
doi: 10.1089/thy.2022.0239. Epub 2022 Oct 20.

Clinicopathologic Characteristics of Pediatric Follicular Variant of Papillary Thyroid Carcinoma Subtypes: A Retrospective Cohort Study

Stephen Halada  1 , Julia A Baran  1 , Andrew J Bauer  1   2 , Julio C Ricarte-Filho  1 , Amber Isaza  1 , Tasleema Patel  1 , Aime T Franco  1 , Sogol Mostoufi-Moab  1   3 , N Scott Adzick  4 , Ken Kazahaya  5   6 , Tricia R Bhatti  7 , Zubair Baloch  7 , Lea F Surrey  7
Affiliations

Clinicopathologic Characteristics of Pediatric Follicular Variant of Papillary Thyroid Carcinoma Subtypes: A Retrospective Cohort Study

Stephen Halada et al. Thyroid. 2022 Nov.

Abstract

Introduction: Follicular patterned thyroid nodules with nuclear features of papillary thyroid carcinoma (PTC) encompass a range of diagnostic categories with varying risks of metastatic behavior. Subtypes include the invasive encapsulated follicular variant of PTC (Ienc-fvPTC) and infiltrative fvPTC (inf-fvPTC), with tumors lacking invasive features classified as noninvasive follicular thyroid neoplasms with papillary-like features (NIFTPs). This study aimed to report the clinical and histological features of pediatric cases meeting criteria for these histological subtypes, with specific focus on Ienc-fvPTC and inf-fvPTC. Methods: In this retrospective cohort study, pediatric patients with thyroid neoplasms showing follicular patterned growth and nuclear features of PTC noted on surgical pathology between January 2010 and January 2021 were retrospectively reviewed and classified according to the recent 2022 World Health Organization (WHO) criteria. Clinical and histopathologic parameters were described for NIFTP, Ienc-fvPTC, and inf-fvPTC subtypes, with specific comparison of Ienc-fvPTC and inf-fvPTC cases. Results: The case cohort included 42 pediatric patients, with 6 (14%), 25 (60%), and 11 (26%) patients meeting criteria for NIFTP, Ienc-fvPTC, and inf-fvPTC, respectively. All cases were rereviewed, and 5 patients originally diagnosed with Ienc-fvPTC before 2017 were reappraised as having NIFTPs. The NIFTP cases were encapsulated tumors without invasive features, lymph node or distant metastasis, or disease recurrence. Ienc-fvPTC tumors demonstrated clearly demarcated tumor capsules and capsular/vascular invasion, while inf-fvPTC tumors displayed infiltrative growth lacking a capsule. inf-fvPTC cases had increased prevalence of malignant preoperative cytology, lymph node metastasis, and distant metastasis (p < 0.01). These cases were treated with total thyroidectomy, lymph node dissection, and subsequent radioactive iodine therapy. Preliminary genetic findings suggest a predominance of fusions in inf-fvPTC cases versus point mutations in Ienc-fvPTC (p = 0.02). Conclusions: Pediatric NIFTP and fvPTC subtypes appear to demonstrate alignment between clinical and histological risk stratification, with indolent behavior in Ienc-fvPTC and invasive features in inf-fvPTC tumors.

Keywords: follicular variant; papillary thyroid carcinoma; pediatrics; thyroid.

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Conflict of interest statement

This research was conducted in the absence of commercial or financial conflicts. A.T.F. is on the Board of Directors for the American Thyroid Association.

Figures

FIG. 1.
FIG. 1.
Cohort selection from patients presenting a follicular pattern between 2010 and 2021. fvPTC, follicular variant of papillary thyroid carcinoma; NIFTP, noninvasive follicular thyroid neoplasm with papillary-like nuclear features; Ienc-fvPTC, invasive encapsulated fvPTC; inf-fvPTC, infiltrative fvPTC.
FIG. 2.
FIG. 2.
Representative preoperative ultrasound images for NIFTP, Ienc-fvPTC, and inf-fvPTC. (A) NIFTP and (B) Ienc-fvPTC displaying nodules with clearly delineated (smooth) margins. (C) inf-fvPTC displaying a nodule with invasive margin (arrow) and punctate echogenic foci (double arrow).
FIG. 3.
FIG. 3.
Representative histological images for NIFTP, Ienc-fvPTC, and inf-fvPTC. (A) NIFTP tumor demonstrating encapsulation without invasion with (B) follicular architecture and notably enlarged overlapping nuclei with chromatin clearing. (C) Ienc-fvPTC tumor demonstrating encapsulation with (D) capsular (top) and vascular (arrow) invasion and (E) nuclear features of PTC. (F) inf-fvPTC tumor demonstrating diffuse involvement without encapsulation and (G) clear cell features.
See this image and copyright information in PMC

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