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

BACKGROUND: 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.

METHODS: 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.

RESULTS: 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.

CONCLUSIONS: 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.