Implications of a Suspicious Afirma Test Result in Thyroid Fine-needle Aspiration Cytology: an Institutional Experience

Background: Fine-needle aspiration (FNA) biopsy is the most frequently used method for thyroid nodule evaluation. However, up to 30% of cases are considered indeterminate. Surgery is typically recommended for these cases, but up to two-thirds of indeterminate cases are found to be benign. The Afirma test is used for the preoperative classification of thyroid nodules with indeterminate cytology. This study reviews the authors' institutional experience with Afirma.

Methods: A cohort of 132 cases of thyroid FNA with Afirma testing was selected from the study files and relevant information was recorded and analyzed. At the study institution, Afirma is mainly performed on atypia of undetermined significance (AUS)/follicular lesion of undetermined significance (FLUS) cases when diagnosed as such on repeat FNA.

Results: The cohort included 98 female (74%) and 34 male (26%) patients. Cytology diagnosis was AUS/FLUS in 68 cases (51.5%), follicular neoplasm (FN) in 39 cases (29.5%), and FN with oncocytic features (FNOF) in 25 cases (19.0%). Of the FNOF cases with suspicious Afirma findings, 2 (15%) were malignant and 11 (85%) were benign. Of the FN cases with suspicious Afirma findings, 9 (53%) were malignant and 8 (47%) were benign. Of the AUS/FLUS cases with suspicious Afirma findings, 10 (63%) were malignant and 6 (37%) were benign.

Conclusions: The Afirma classifier is a useful tool to aid in the distinction of cytologically indeterminate nodules. Performing Afirma in cases diagnosed as AUS/FLUS on repeat FNA would increase the positive predictive value, thereby minimizing the number of benign cases referred to surgery. Results of the Afirma test could be limited in cases diagnosed as FNOF.