Implications of a Suspicious Afirma Test Result in Thyroid Fine-Needle Aspiration Cytology: An Institutional Experience Ricardo R. Lastra, MD; Michelle R. Pramick, MD; Cody J. Crammer, BS; Virginia A. LiVolsi, MD; and Zubair W. Baloch, MD, PhD
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. Cancer (Cancer Cytopathol) C 2014 American Cancer Society. 2014;122:737-44. V
KEY WORDS: thyroid; Afirma; fine-needle aspiration; cytology; molecular.
INTRODUCTION Fine-needle aspiration (FNA) biopsy is the most widely used method for the screening and diagnosis of thyroid nodules. In most instances, the FNA results are either definitely benign or malignant, allowing for appropriate action. However, between 15% to 30% of cases are considered indeterminate.1 As per the Bethesda System for Reporting Thyroid Cytopathology, indeterminate diagnostic categories include “atypia of undetermined significance (AUS)/follicular lesion of undetermined significance (FLUS)” “follicular neoplasm or suspicious for follicular neoplasm (FN),” and “suspicious for malignancy.”2,3 Because the possibility of malignancy cannot be excluded in indeterminate cases, surgery is typically recommended; however, up to two-thirds of these cases are found to be benign at the time of surgical resection.1,4 This results in unnecessary surgical procedures, complications, and morbidity, as well as medical expenses. Corresponding author: Ricardo R. Lastra, MD, Department of Pathology and Laboratory Medicine, Hospital of the University of Pennsylvania, 3400 Spruce St, 6 Founders, Hospital of the University of Pennsylvania, Philadelphia, PA 19104; Fax: (215) 349-8994; [email protected]
Department of Pathology and Laboratory Medicine, Hospital of the University of Pennsylvania, Philadelphia, Pennsylvania See editorial on pages 715-9, this issue. Received: May 1, 2014; Revised: May 27, 2014; Accepted: May 28, 2014 Published online August 13, 2014 in Wiley Online Library (wileyonlinelibrary.com) DOI: 10.1002/cncy.21455, wileyonlinelibrary.com
Molecular testing of indeterminate thyroid nodules as an adjunct to thyroid cytology has been proven to be of significant value.5 Moreover, it is considered a cost-reducing proposition, particularly due to the reduction in 2-stage thyroidectomy (lobectomy followed by completion thyroidectomy).6 The Afirma gene expression classifier is a proprietary diagnostic test developed by Veracyte Inc. (South San Francisco, Calif) for the preoperative identification of benign thyroid nodules with a cytology diagnosis of AUS/FLUS and FN. The assay analyzes the mRNA expression of 167 genes to identify the signature of a benign thyroid nodule. Based on this information, it classifies nodules as either “benign” (95% negative predictive value [NPV] for aspirates classified as AUS/FLUS and 94% for aspirates classified as FN) or “suspicious” for malignancy (>50% risk for malignancy).7 Thus, the Afirma gene expression classifier can be used to identify a subpopulation of patients with a low probability of malignancy in a population of patients for whom surgery would be recommended. Although the usefulness of Afirma appears to be evident in the preoperative triage of thyroid nodules with indeterminate cytology, to our knowledge only a limited number of studies have evaluated its use in the clinical setting.8 In the current study, we reviewed our experience with the Afirma gene expression classifier when applied to thyroid nodules with an indeterminate cytology in an attempt to validate its usefulness at the study institution.
MATERIALS AND METHODS The institutional pathology files at the Hospital of the University of Pennsylvania were retrospectively searched for all thyroid FNA cases with a diagnosis of AUS/FLUS, FN, or follicular neoplasm with oncocytic features (FNOF) and concurrent Afirma results from February 2011 to January 2014. At this institution, a total of 5 cytopathologists evaluate thyroid FNA specimens. The overall laboratory rates regarding thyroid nodule FNAs is as follows: nondiagnostic, 1%; benign, 60%; AUS/FLUS, 11.5%; FN, 12.2%; FNOF, 5.2%; suspicious for malignancy, 3%; and malignant, 7.1%. Ultrasonographic features considered as “worrisome,” and that triggered biopsy included hypervascularity, calcifications, and increasing size (as compared with prior studies). The collected data points included patient demographic data (age and sex), as well as the ultrasonographic characteristics of the biopsied nodule, including size, 738
laterality, echogenicity, vascularity, and the presence of calcifications. The prominent cytomorphologic features that resulted in a nodule being diagnosed as AUS/FLUS were recorded and categorized into 4 categories as follows: category 1: the presence of follicular cell groups with crowding and overlapping in a benign-appearing background; category 2: the presence of follicular cell groups with crowding and overlapping in a scant specimen; category 3: the presence of follicular cell groups with crowding and overlapping in a background of lymphocytic thyroiditis; and category 4: other (which included focally present nuclear atypia, nuclear grooves, and elongation, but which were not enough for a diagnosis of “suspicious for malignancy” or “papillary thyroid carcinoma”). When either partial/ hemithyroidectomy or total thyroidectomy were performed subsequent to the FNA, the final surgical pathology diagnosis of the biopsied nodule was also collected. In each case, FNA was performed under ultrasound guidance by a radiologist and/or endocrinologist, most often with a 27-gauge needle. The initial 2 passes were evaluated on-site by a cytopathologist, who confirmed the presence of adequate material for diagnosis and rendered a preliminary diagnostic impression. Up to 2 additional passes were obtained in any given case, if it was believed that the original attempts were unsuccessful. Based on on-site interpretation of the cytopathologists and the clinical and radiologic impression of the performing clinician, additional pass(es) was performed exclusively for Afirma testing. As a general rule in the study institution, on-site diagnosis of AUS/FLUS in a repeat FNA of a nodule initially diagnosed as AUS/FLUS on first FNA triggers an additional pass for Afirma testing. No set criteria exist for the Afirma testing of nodules with a preliminary diagnosis FN or FNOF. However, an onsite or final diagnosis of FN or FNOF in cases of small and radiologically benign-appearing nodules usually also leads to Afirma testing. Statistical Analysis
Statistical analyses were performed using the chi-square test. A P value of