Has Afirma gene expression classifier testing refined the indeterminate thyroid category in cytology?

Thyroid fine-needle aspiration (FNA) plays a pivotal role in the evaluation of thyroid nodules. Up to 30% of cases are diagnosed as indeterminate by FNA, including atypia of undetermined significance, follicular lesion of undetermined significance, suspicious for a follicular neoplasm, and follicular neoplasm, with approximately two-thirds having a benign outcome. The gene expression classifier (GEC) test is a molecular test for cases with indeterminate cytology. The purpose of the current study was to examine the refining role of the GEC test within a single institution.

Retrospective analysis of all thyroid FNAs during a 20-month period after implementation of GEC was performed. Cases of indeterminate cytology with concomitant GEC testing were selected and divided further in 4 subgroups. Correlation with surgical follow-up, when available, was performed. The results were compared with previously published data from the study institution before the implementation of GEC testing.

Among the 217 cases, there were 189 with indeterminate cytology, 42% of which were benign and 50% of which were suspicious by GEC. The excisional rate of atypia of undetermined significance-follicular lesion of undetermined significance in the pre-GEC category was 63%, which decreased to 35% in the post-GEC category, whereas the malignancy rate in the excised thyroids increased from 35% in the pre-GEC category to 47% in the post-GEC category. Similar findings also were obtained for suspicious for a follicular neoplasm-follicular neoplasm lesions.

The strength of the GEC test appears to lie in its ability to reclassify 42% of indeterminate cytology cases as benign, thereby decreasing the number of unnecessary surgical procedures.