Diagnostic category

Risk of thyroid cancer

Most common histologic diagnoses

Indications for repeated FNAB

Commonly recommended managementa

I: Nondiagnostic

5%-20%c,d

Any diagnosis possible

Repeated FNB with US guidance at any time, depending on risk; in case of clinical suspicion of anaplastic cancer, further diagnostics must be continued immediately

Indications for surgery depend on clinical risk of malignancy; nondiagnostic biopsy likely in patients with cysts or thyroiditis

II: Benign

0%-7%c,d

Multinodular goiter, including hyperplastic nodules and colloid nodules; thyroiditis

No (except in cases of new US risk factors of suspicious lymphadenopathy or TIRADS-5 nodule with prior benign FNAB result)

Follow-up (clinical and US)

III: AUS

15%-30%c

Category used only if accurate cytologic diagnosis not possible

Yes; FNAB can be repeated at any time point (there is no longer need to wait 3-12 months)

Possible options: (1) molecular testing (if available); (2) active surveillance; (3) surgery

IV: Follicular neoplasma

23%-34%b,d

May reflect a benign tumor, which cannot be differentiated from malignancy by cytology alone

No

Possible options: (1) molecular testing (if available); (2) active surveillance; (3) surgery

V: Suspicious for malignancy

67%-83%c,d

Suspected thyroid cancer

No

Surgery

VI: Malignant

97%-100%d

Papillary thyroid cancer; medullary thyroid cancer; anaplastic thyroid cancer; other malignancy

No

Surgery

a Actual management also depends on other clinical and US risk factors.

b The diagnosis of follicular neoplasm includes nodules “suspicious for oxyphil neoplasm,” which is more frequently an unequivocal indication for surgery.

c Risk of malignancy if NIFTP is excluded because it is benign; previously classified as noninvasive follicular variant of papillary thyroid carcinoma.

d Risk of malignancy if NIFTP is included.

Note that the risk of thyroid cancer based on each Bethesda category will also vary from institution to institution.