Differentiated thyroid cancer and Hashimoto thyroiditis: Utility of the Afirma gene expression classifier

Background and Objectives The Afirma gene expression classifier (AGEC) has not been tested or validated in a high-risk group, such as patients with Hashimoto's thyroiditis (HT). We hypothesized that AGEC would perform worse in patients with HT. Methods A retrospective review of patient charts in a single academic institution who underwent thyroidectomy between 2012 and 2017 was conducted. Patients with HT who underwent AGEC were identified to calculate sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV). Results We identified 69 patients with HT and atypia of undetermined significance/follicular lesion of undetermined significance (AUS/FLUS) on cytology who underwent AGEC analysis. The mean age of AGEC cohort was 50 years (range, 26-77 years) with 90% female. The median nodule size was 1.9 cm (interquartile range [IQR], 1.2-2.7 cm). Of the 69 patients, 62 showed suspicious AGEC of which 26 showed TC on surgical pathology. Of the seven benign AGEC, two showed TC on surgical pathology. The sensitivity, specificity, PPV, and NPV were 93%, 12%, 42%, and 71%, respectively. Of the entire AGEC cohort, 17 (43%) showed multicentric disease. Conclusions We observed a lower NPV for AGEC to rule out thyroid cancer in patients with HT, which reduces the utility of the test for this population.