Diagnostic category

Risk of thyroid cancer

Most common histologic diagnoses

Indications for repeated FNB

Commonly recommended managementa

I: Nondiagnostic biopsy

5%-10%c,d

Any diagnosis possible

Repeated FNB with US guidance, usually in 3-12 months, 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%-3%c,d

Multinodular goiter, including hyperplastic nodules and colloid nodules; thyroiditis

No (except in cases of new US risk factors of suspicious lymphadenopathy)

Follow-up (clinical and US)

III: AUS or FLUS

6%-18%c (10%-30%)d

Category used only if accurate cytologic diagnosis not possible

Yes (in 3-12 months, depending on risk)

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

IV: Suspicious for follicular neoplasma

10%-40%b,c (25%-40%)d

May reflect nonneoplastic lesion or benign tumor, which cannot be differentiated from malignancy by cytology alone

No but if surgery is planned diagnosis must be confirmed by another cytologist

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

V: Suspicious for malignancy

45%-60%c (50%-75%)d

Suspected thyroid cancer

No but diagnosis must be confirmed by another cytologist

Surgery

VI: Malignant

94%-96%c (97%-99%)d

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

No but diagnosis must be confirmed by another cytologist

Surgery

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

b The diagnosis of nodules “suspicious for follicular neoplasm” includes those “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.