MON-511 Are Thyroid Nodule Fine Needle Aspiration Washings an Acceptable Alternative to Dedicated Fine Needle Aspirates When Obtaining Tissue Samples for Genetic Expression Classifier Analysis?

The Bethesda System for Reporting Thyroid Cytopathology stratifies thyroid nodules by risk associations. Approximately 15-30% of fine needle aspirations (FNA) fall into an indeterminate criteria, and two thirds are found to be surgically benign leading to unnecessary surgeries (1). Veracyte Inc. developed the Afirma gene expression classifier (GEC) to identify whether an indeterminate nodule had benign expression, with a NPV of 95% for AUS/FLUS (Atypia of undetermined significance/ follicular lesion of undetermined significance) nodules making it an excellent way to rule out malignancy (2). The goal of testing for thyroid cytology includes avoiding unnecessary surgery in benign nodules and identifying high risk from low risk lesions. The Afirma validation landmark study aided in the commercial approval for use in clinical practice after showing a 95.1% sample sufficiency when 2 dedicated samples were obtained in addition to the 3-5 FNA samples for cytology, but our institutional practice habits may suggest other techniques may be valid as well (2). We aimed to assess the rate of sufficient sample for GEC based on FNA washings at our institution, without using dedicated FNA for GEC. Data was gathered from all indeterminate nodule FNA washings referred for Afirma GEC from January 2015 through December 2017. Samples were determined on Afirma report as benign, suspicious, or insufficient and rate of insufficiency was determined. 95 indeterminate nodule FNA washings were sent for Afirma GEC. 93 (97.9%) samples were sufficient for RNA, with 47 (49.5%) reported as suspicious and 46 (48.4%) reported as benign, 2 (2.1%) samples were insufficient for RNA. 97.9% of our samples were sufficient when using FNA washings alone. Our experience suggests that the technique used at our clinical practice is an acceptable alternative to using an additional 2 passes for dedicated samples in collecting RNA for Afirma GEC. This method decreases need for call back for a second biopsy, is less time consuming, and potentially more cost effective. Limitations in our study are a small sample size limited to a single institution, differing number of FNA washings per total passes among practitioners, and variability of experience between providers. In conclusion thyroid nodule FNA washings are an acceptable alternative to dedicated FNA when obtaining tissue samples for genetic expression classifier analysis. Further studies with a larger sample size across different institutions are necessary. 1.Prathima S, Thyroid Research and Practice, January-April 2016; Vol 13: Issue 1; p 9-14 Yang SE et al, Cancer Cytopathology, February 2016, p 100-109 2. Alexander EK. Kennedy GC. Baloch ZW.et al. Preoperative diagnosis of benign thyroid nodules with indeterminate cytology. N Engl J Med. 2012;367(8):705–715.