82nd Annual Meeting of the American Thyroid Association:

How Accurate Is This Gene Expression Classifier?

For most thyroid nodules, fine-needle aspiration is an accurate diagnostic tool.  However, as is well-known, there are some nodules that return a result of “indeterminate cytology” on fine-needle aspiration; they may also be “suspicious for follicular neoplasm.”  For those nodules (10%-25%), surgery is required to make a definitive diagnosis.

In order to try to reduce this number of surgeries, a new Gene Expression Classifier (GEC) has been developed—Afirma (made by Veracyte).  This GEC is supposed to help determine which nodules are benign without surgery.  Using GEC, about 50% of indeterminate nodules are proved benign; initial reports say that this test has a 96% negative predictive value.

Doctors at the Mayo Clinic recently did an independent study of the Afirma GEC, and they reported their initial findings in a presentation on September 22, 2012, at the American Thyroid Association Annual Meeting.

How the GEC Was Used at the Mayo Clinic
The Mayo Clinic started using this GEC in May 2011; it was phased in, and they used their own cytopathology to determine which samples were appropriate for GEC testing.

If an FNA biopsy was returned as “indeterminate,” the patient was offered GEC testing.  If that test was returned as suspicious, thyroid surgery was recommended; if it was benign, the patient was offered ultrasound follow-up.

For all patients who had surgery, their surgical and pathology reports were reviewed.

The Mayo Clinic’s Experience with the GEC
There were 1,014 nodules that were biopsied (from 771 patients).  Of those, 807 (79.5%) were cytologically benign, and 75 (7.4%) were malignant or suspicious for malignancy.  There were 68 indeterminate samples, and 44 of the patients with indeterminate samples consented to GEC analysis.

Of those samples used in GEC analysis, 6 (13.6%) yielded no information.  A benign result was seen in 10 (26%) of the remaining samples.  Nine of those patients chose ultrasound follow-up, but one chose surgery for cosmesis.

There were 28 GEC suspicious nodules, and the Mayo Clinic has operated on 23 of those (82%) of those.  Malignancy was confirmed in 3 patients (13%); there was one case each of papillary, follicular, and Hurthle cell carcinoma.

Comparing the Mayo Clinic’s Results with Previously Reported Results
This initial report showed a lower-than-previously-reported rate of GEC benign samples; the Mayo Clinic showed 26%, while previous reports showed 53% (p < 0.01).

Additionally, the Mayo Clinic reported a lower rate of malignancy in those nodules that are GEC suspicious.  They found 13%, versus 38% of previous reports (p < 0.01).

This clinical application of this GEC test suggests that more independent confirmatory studies should be done on this before there is widespread use of this (or any other) molecular adjunct to cytopathology for thyroid.

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