Impact of the modification of the diagnostic criteria in the 2017 Bethesda System for Reporting Thyroid Cytopathology: a report of a single institution in Japan

Abstract

The Bethesda System for Reporting Thyroid Cytopathology has recently been revised in 2017 (TBSRTC 2017). This study aimed to evaluate the impact of modifying the diagnostic criteria in TBSRTC 2017 at a single institute. We retrospectively reviewed cytological specimens of 10,399 thyroid nodules submitted for thyroid fine-needle aspiration cytology. Among them, 56 atypia of undetermined significance or follicular lesion of undetermined significance (AUS/FLUS) nodules, 16 suspicious for malignancy (SFM) nodules, and 8 malignant nodules were re-categorized into follicular neoplasm or suspicious for a follicular neoplasm (FN/SFN). The incidence of FN/SFN was increased by 0.8%, while that of AUS/ FLUS, SFM, and malignant nodule was decreased by 0.5%, 0.2%, and 0.1%, respectively. In nine (60%) of the 15 nodules that were re-classified from AUS/FLUS to FN/SFN nodules and re-aspiration was performed, it was possible to judge whether they were benign or malignant. Of the 24 patients with FN/SFN nodules originally diagnosed with SFM or malignant, 16 were followed up without surgical resection. In conclusion, TBSRTC 2017 only caused minor changes in the incidence of each diagnostic category. TBSRTC 2017 was revised to avoid false positives owing to noninvasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP) that account for >10% of papillary thyroid carcinomas; however, it is not necessary in low frequency NIFTP institutes or countries. In Japan, we propose active surveillance as an accepted option for clinically managing AUS/FLUS, FN/SFN, SFM, or malignant nodules having favorable benign clinical findings or being part of the low-risk group.

Important cytological findings for distinction between follicular variant and conventional papillary thyroid carcinoma, including noninvasive follicular thyroid tumors with papillary-like nuclear features

“…Clinicians are also able to prevent overtreatment by considering not only cytological diagnosis but also ultrasound findings. Higuchi M, et al [27] reported that active surveillance (follow-up without surgical resection) is an acceptable option for thyroid nodules having favorable benign clinical findings or benign part of the lowrisk group.…”

False positive cases in thyroid cytopathology – the experience of a single laboratory and a systematic review

“…TBSRTC recommends that in cases where morphology raises the possibility of NIFTP (microfollicular architecture, lack of papillary structures, partial PTC nuclear features) an educational note should be added. It is yet to be determined whether ancillary studies would be able to distinguish between NIFTP and other morphologically similar tumours that exhibit more aggressive behaviour 7,40 …”

Diagnostic significance of apical membranous and cytoplasmic dot-like CD26 expression in encapsulated follicular variant of papillary thyroid carcinoma: a useful marker for capsular invasion

“…Therefore, the diagnosis of non-invasive type EFV-PTC has been reframed as NIFTP [7]. However, it is difficult to morphologically distinguish the presence or absence of invasion, pre-operatively, besides the observer-associated variations in the identification of nuclear features of PTC [8,33,34]. Identification of a suitable marker that can distinguish between the presence and absence of invasion would significantly contribute to the reduction of excision region as well as in precise treatment.…”