Indeterminate fine-needle aspiration biopsy of the thyroid: identification of subgroups at high risk for invasive carcinoma.

BACKGROUND: We examined the various cytologic features of indeterminate thyroid fine-needle aspirates along with known clinical and radiologic risk factors to determine whether any parameters were predictive of malignancy.
METHODS: Indeterminate fine-needle aspirates were prospectively categorized into four subgroups: (1) suspicious for papillary carcinoma, (2) follicular neoplasm, (3) Hürthle cell neoplasm, and (4) hypercellular follicular aspirates with colloid. Several clinical risk factors were examined, and subgroup comparisons were performed with Fisher's exact test.
RESULTS: Of 571 fine-needle aspirate cytologic findings 104 were interpreted as indeterminate for malignancy, and 81 patients underwent thyroidectomy. Invasive cancer was diagnosed in 9 of 10 lesions cytologically suspicious for papillary carcinoma, 8 of 43 follicular neoplasms, 5 of 18 Hürthle cell neoplasms, and 0 of 10 hypercellular aspirates. Cytologic subgroup (p < 0.0001) and age of 50 years or older (p = 0.008) were the only significant predictors of malignancy. When used together, age of 50 years or older and a cytologic diagnosis of follicular or Hürthle cell neoplasm also identified a subgroup of patients at high risk (9 of 20) of invasive malignancy (p = 0.01).
CONCLUSIONS: The majority of invasive cancers (18 of 22, 82%) were found in patients whose lesions were suspicious for papillary carcinoma or in patients 50 years or older with follicular or Hürthle cell neoplasms. The risk of carcinoma in these combined subgroups (18 of 30, 60%) warrants early surgical intervention.