Objective: The Veracyte Afirma Gene Expression Classifier (GEC) has been the most widely used negative predictive value molecular classifier for indeterminate cytology thyroid nodules since January 2011. To improve the specificity and further reduce unnecessary thyroid surgeries, a second-generation assay (Afirma Genetic Sequence Classifier [GSC]) was released for clinical use in August 2017. We report 11 months of clinical outcomes experience with the GSC and compare them to our 6.5-year experience with the GEC.
Methods: We searched our practice registry for FNAB nodules with Afirma results from January 2011through June 2018. GEC versus GSC results were compared overall, in oncocytic and nononcocytic aspirates and by pathologic outcomes.
Results: GSC identified less indeterminate cytology nodules as suspicious (38.8%; 54/139) when compared to GEC (58.4%; 281/481). There was a decrease of in the percentage of oncocytic fine-needle aspiration thyroid biopsy (FNAB) subjects classified as suspicious in the GSC group, with 86 of 104 oncocytic indeterminates (82.7%) classified as suspicious by GEC and 12 of 34 (35.3%) classified as suspicious by GSC. The surgery rate in patients with oncocytic aspirates fell from 56% in the GEC group to 31% in the GSC-evaluated group (45%). Pathology analysis demonstrated a false-negative percentage for an incomplete surgical group of 9.5% for GEC and 1.2% for GSC.
Conclusion: Our GSC data suggest that the GSC further reduces surgery in indeterminate thyroid nodules by improving the specificity of Afirma technology without compromising sensitivity. A primary determinant for this change is a significant improvement in the specificity of the Afirma GSC test in oncocytic FNAB aspirates.
Abbreviations: FNAB = fine-needle aspiration biopsy; GEC = Gene Expression Classifier; GSC = Genetic Sequence Classifier.