Bethesda Grade (1-6)

Reporting

I — Non-diagnostic / Unsatisfactory

II — Benign

III — Atypia of Undetermined Significance (AUS) / Follicular Lesion of Undetermined Significance (FLUS)

The grayest of gray zones. Slight atypia, not clearly benign or suspicious. Cancer risk: modest, variable.

IV — Follicular Neoplasm / Suspicious for Follicular Neoplasm

Architecture suggests a follicular tumor. You can’t call cancer on cytology because capsular/vascular invasion can’t be seen. Cancer risk: intermediate.

V — Suspicious for Malignancy

Cytology strongly leans malignant but not enough to call it outright. Cancer risk: high.

VI — Malignant

Clear cytologic features of malignancy — classically papillary thyroid carcinoma. Cancer risk: essentially certain.

Number	Diagnostic Category	Condition	Next Step	Estimated/predicted risk of malignancy by the Bethesda system, %a	Actual risk of malignancy in nodules surgically excised, % median (range)b
I	Non-diagnostic	Unsatisfactory sample	Repeat FNA	1–4	20 (9–32)
II	Benign	nodular hyperplasia or thyroiditis	Clinical & US follow up	0–3	2.5 (1–10)
III	AUS	dysplasia, maybe follicular adenoma	Repeat FNA, molecular testing, diagnostic lobectomy/surveillance	5–15	14 (6–48)
IV	FN (Follicular Neoplasm)	may be follicular adenoma	molecular testing, diagnostic lobectomy	15–30	25 (14–34)
V	SFM (Suspicious for Malignancy)	Maybe papillary Ca, medullary Ca, lymphoma, met	molecular testing, diagnostic lobectomy or near-total thyroidectomy	60–75	70 (53–97)
VI	Malignant	papillary Ca, follicular Ca, medullary Ca, anaplastic Ca, lymphoma, met, SCC	lobectomy or near-total thyroidectomy	97–99	99 (94–100)