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Classifier preoperatively identified medullary thyroid cancer
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LAS VEGAS — Preoperative genomic identification of medullary thyroid cancer could alter patient care and allow for more informed treatment decisions at earlier stages, according to research presented at the AACE 23rd Annual Scientific & Clinical Congress.
In the largest thyroid fine-needle aspiration biopsy (FNAB) study evaluating the incidence of medullary thyroid cancer (MTC) to date, Richard Kloos, MD, of Veractye, Inc., and colleagues prospectively conducted cytology on 50,430 consecutively received thyroid nodule FNAB samples.
“While our goal includes reducing unnecessary diagnostic surgery,” Kloos said, “another goal is to help patients get the correct surgery the first time.”
Among the 15.5% indeterminate samples (Bethesda categories III and IV), the researchers performed the Afirma Gene Expression Classifier (GEC) to reclassify samples as benign or suspicious. They also identified MTC using the MTC Classifier.
By locally read cytopathology, the scientists evaluated an additional 2,673 prospective FNAB samples identified as indeterminate, suspicious or malignant (Bethesda III-VI). Clinical information was gathered for patients with either MTC signatures or cytological features that suggested MTC. The researchers used the MTC Classifier on 215 consecutive likely malignant specimens (Bethesda V-VI) to calculate incidence of the MTC signature.
MTC signatures were identified in 0.2%, 0.5%, 1.0% and 1.8% of consecutive nodules with Bethesda category III-VI cytologies, respectively. The positive predictive value for the MTC Classifier was 98%; the single false positive was another neuroendocrine tumor (paraganglioma).
Basal serum calcitonin was <20 pg/ml in 7.5% in MTC-confirmed patients, and unsuspected MEN2 germline mutations were identified in 10%. No MTC was found in five cases where cytology raised suspicion for MTC but the MTC Classifier did not, which suggests a high negative predictive value.
For more information: Kloos R. Abstract 1100. Presented at: AACE 23rd Annual Scientific & Clinical Congress; May 13-18, 2014; Las Vegas, Nevada.
Disclosures: Kloos is an employee of Veracyte, Inc.
Perspective
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Christian Nasr, MD
This constitutes a significant breakthrough, given the volume of the database accumulated by the researchers. At present, medullary thyroid cancer (MTC) is diagnosed either by fine needle aspiration biopsy (FNAB) or examination after surgery. FNAB specimens yielding atypia will usually lead to repeating the procedure to try to arrive at a diagnosis. The health care provider will usually recommend removing the thyroid lobe that contains the nodule to obtain a diagnosis and, if cancer is proven, then the rest of the thyroid will have to come out (a second surgery).
What Kloos et al are suggesting is that their test will provide an accurate diagnosis of MTC the very first time around and the patient will end up having the correct initial surgery. Two concerns: the Afirma GEC was not designed for this application, however this fortuitous finding might offer patients great benefit but more studies are needed. Also, the test is expensive, which prohibits widespread application; a reduction of the cost will help it compete with other diagnostic methods.
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