Correlating thyroid cytology and histopathology: Implications for molecular testing

Abstract

Background A gene expression classifier (GEC) has been advocated in management of some indeterminate nodules without surgery. We assessed the potential negative predictive value (NPV) of the GEC at our academic center. Methods Retrospectively, all cytologically indeterminate fine-needle aspirates (FNAs) diagnosed by University of Iowa cytopathologists over a 3-year period were identified. Histopathologic findings were recorded. Using published sensitivity and specificity, NPVs were calculated. Results Of 178 nodules (17, 135, and 26 in classes III, IV, and V, respectively), 71 (40%) were malignant. Prevalence of malignancy was 41%, 29%, and 96% for classes III, IV, and V, respectively. Using sensitivities and specificities for the GEC, NPVs were 91% for the cohort: 88%, 92%, and 26% for classes III, IV, and V, respectively. Conclusion Molecular testing should be associated with an NPV no lower than that from clinical criteria alone. With the prevalences reported, GEC use may result in more missed cancer diagnoses.