Thyroid nodule size linked to malignancy risk

Patients with a nondecisive fine-needle aspiration for large nondiagnostic thyroid nodules or lesions of undetermined significance should be considered for surgery because more than half of these large nodules can be malignant.

In a review of 156 patients with nondecisive fine-needle aspirations (FNAs), nodule size was a major determinant in surgical referral, “Nodules of this size were associated with a malignancy rate of up to 60%.”

FNA is considered the main diagnostic tool in deciding which patients to refer to surgery. However, the FNA results may not be helpful when the cytology specimen is nondiagnostic or qualifies as a follicular lesion of undetermined significance — both classifications that are part of the new six-level FNA classification system suggested by the National Cancer Institute.

When an FNA comes back as nondecisive on such specimens, the clinician must choose between surgery and clinical follow-up as the next step. Unfortunately, there are no hard-and-fast rules about which of the two management paths to choose.

Molecular markers are becoming more important in the decision, but can’t be relied upon in every patient. When these markers are present in high concentrations, they are up to 99% accurate in identifying malignant nodules and so are a very helpful tool. But only 40% of nodules are positive for these risk markers, so we still have an unmet need of what to do with many other patients.

Out of nearly 500 tests, 156 were nondecisive. Of these specimen, 90 (58%) were classified as follicular lesion of undetermined significance (FLUS) and 66 (42%) as nondiagnostic.

Overall, 104 patients had a thyroidectomy (775 of the FLUS group and 525 of the nondiagnostic group). The rest of the patients were followed clinically. The rate of malignancy was 41% in the FLUS patients and 325 in the nondiagnostic patients.

Among those with FLUS who had surgery, 50% had no other clinical indication for surgery except the nondecisive FNA. The most common documented indication was a nodule size of 3 cm or larger in 29%. Other indications — each of which accounted for less than 5% — were male gender, a family history of thyroid cancer, exposure to radiation, and a suspicious ultrasound exam.

In the nondiagnostic group all of those who went for surgery had other indications. The most common one was a cold thyroid scan 31. Other indication were nodule size (20%), micro calcifications on ultrasound (16%), and a history of radiation exposure (15%) indication that did not specify accounted for the remaining 18%.

Half of all patients for whom nodule size was the documented surgical indication had clinically significant thyroid cancer. When we compared the surgical and clinical follow-up groups, we found that 60% of the surgical group had a lesion 3 cm or larger, compared with 29% of the follow-up group, so clearly, when clinicians found a large lesion, most of them were referred to surgery.