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Oncocytic cells, also known as Hürthle cells, are present in more than 20% of indeterminate thyroid nodules and are often challenging to classify as high or low risk. 1,2,3 Due to an abundance of oncocytic cells, both oncocytic carcinomas and adenomas share a similar cytologic appearance. 4 Therefore, diagnosis has historically relied on identifying capsular and vascular invasion, which can be challenging to diagnose in instances of minimally invasive disease. 5
To address this challenge, Veracyte’s Afirma Genomic Sequencing Classifier (GSC) includes two algorithmic components that are able to classify oncocytic cell lesions with high sensitivity. 1,6
First is the Oncocytic Cell Index , which uses mRNA expression and mitochondrial transcripts to identify fine needle aspiration (FNA) samples with a genomic signature associated with oncocytic features. Oncocytes contain more mitochondria than normal follicular cells, and mitochondria have their own genome that is separate from the nuclear genome. 5 The RNA sequencing performed by Veracyte allows us to capture and quantify from a molecular perspective if patient samples are oncocytic or not.
The second index is the Oncocytic Neoplasm Index , which leverages mRNA expression and chromosomal loss of heterozygosity (LOH) to identify if a nodule with oncocytic cells is also molecularly neoplastic. Research has shown that oncocytic neoplasms have higher levels of LOH than other subtypes. 7
The result of these two indices is an 89% sensitivity in classifying oncocytic cell lesions which is important to know because about three out of four oncocytic cell lesions are classified as benign . 1,2,3,6,7,8,9,10 Together, these indices have helped improve the specificity and PPV of the benign vs. suspicious call that the Afirma GSC ensemble classifier provides. 1,2,9,10 The performance of Afirma GSC in this subset of challenging nodules has not only been demonstrated in Afirma GSC’s validation study, but has been confirmed in multiple other studies as well. 1,2,6,7,9,10 By addressing the challenge in diagnosing this particular neoplasm, Veracyte aims to improve outcomes for patients.