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Outcomes of “Atypia of Uncertain Significance” in Thyroid Fine Needle Aspiration Cytology: A Six-year Institutional Review
S70 aspiration biopsies (FNABs) of thyroid nodules, and reporting such specimens was not originally addressed by The Bethesda System for Reporting Thyroid Cytopathology (TBSRTC). We correlate their biologic behavior with their corresponding benign cytologic appearance through clinical, radiographic, and surgical followup. Materials and Methods: The pathology archives of 3 large tertiary hospitals were searched between 1997 and 2017 for thyroid FNABs consisting of mature squamous cells without atypia. We reviewed all available slides and included only cases that were moderately to highly cellular; non-atypical nucleated or anucleate squamous cells comprised the vast majority of the cellularity. Available clinical information and/or thyroid ultrasound examination(s) were reviewed by either an endocrinologist or radiologist, respectively. Results: 18 patients (7 men, 11 women) with 20 nodules met the prespecified inclusion criteria. The mean age was 55 years (range 19-76 years). Eight nodules were on the left, nine on the right, and three were midline. The average size was 2.1 cm. Common sonographic characteristics of the 14 nodules with ultrasound images available for review included welldefined appearance (14), lack of internal vascularity (14), thin outer wall (13), general hypoechogenicity (10) with low-intermediate internal echoes (12), and posterior acoustic enhancement (12). Clinical and radiographic followup (mean 4.2 years, range <1 to 9 years) was available for an additional 9 patients, and all nodules were stable during the followup period. All 4 cases with histologic followup were benign squamous-lined cysts. Conclusion: Our findings suggest that thyroid FNABs comprised almost exclusively of mature squamous cells can be reported as benign and managed per standard guidelines for benign nodules. We also propose that the TBSRTC include the pattern of abundant mature, benign-appearing squamous cells in the “Benign” category. PST165 Outcomes of “Atypia of Uncertain Significance” in Thyroid Fine Needle Aspiration Cytology: A Six-year Institutional Review Zarine Kamaluddin, MD, Cecilia Clement, MD. University of Texas Medical Branch, Galveston, TX Introduction: Atypia of uncertain significance (AUS) / follicular lesion of uncertain significance (FLUS) is a category of the Bethesda system (TBS) for reporting thyroid cytology. It is used in certain scenarios where the architectural and nuclear atypia is not sufficient to categorize them as “suspicious for malignancy” or “malignant,” two more diagnostic
Abstracts categories of the thyroid system. The risk of malignancy in a thyroid lesion categorized as AUS is 5%-15%. The goal of our study is to assess the outcome of AUS at our institution. Materials and Methods: We reviewed six years of our archives (Jan 2010 December 2016). All thyroid fine needle aspirations with the diagnosis of AUS were selected. Their results on resection were reviewed. Results: Out of a total of 1,987 thyroid FNAs that were performed, 120 were diagnosed as AUS (6%). Only 53 AUS cases (44%) underwent a resection procedure, and 66 were lost to follow-up / did not undergo surgery. Of the 53 resection specimens, 12 were diagnosed with malignancy (22%). Seven patients had benign diagnoses on repeat FNA. One patient died. (Table). Conclusion: Although our AUS diagnosis rate is low (6%), our rate of malignant diagnosis on resection specimen for these cases is 22%, which is above the estimated risk of malignancy according to the Bethesda system.
PST166 Hurthle Cell Predominance Impacts Results of GEC and Molecular Panel Performance in Indeterminate Thyroid Nodules Shobha Parajuli, MD, Rachel Jug, MD, Sara Ahmadi, MD, Xiaoyin Jiang, MD. Duke University Medical Center, Durham, NC Introduction: Molecular tests such as the Afirma Gene Expression Classifier (GEC) and mutational panels (such as Thyroseq) have been introduced to help risk stratify the cytologically-indeterminate thyroid nodule, with the aim to reduce the number of unnecessary thyroidectomies. Some reports have suggested that samples with Hurthle cell predominance may have a higher false-positive rate on GEC testing, but the data are limited, and little is known about the impact of Hurthle cells on molecular panel performance. Materials and Methods: We reviewed indeterminate (Bethesda III/IV) thyroid nodules from June 2012 through August 2016. Patient demographics, cytology diagnosis, presence of Hurthle cells, molecular test results, and histopathologic diagnosis were collected. Patients who had no result or whose result indicated parathyroid tissue were excluded. Results: The Afirma GEC was performed on 208 patients and ThyroSeq was performed on 96 patients. In the GEC cohort (Table 1), 66% of nodules with Hurthle cells yielded a “suspicious result” versus 47% of nodules without significant Hurthle cells, with a risk of malignancy (ROM) of 18% and 35%, respectively. In the Thyroseq cohort (Table 2), 11% of nodules with Hurthle cells yielded a high risk mutation versus 20% of nodules without significant Hurthle cells, with a ROM of 50% and 7%, respectively. Conclusions: For the molecular panel, while it did not appear that there was an increase in the rate of high-risk mutations being detected in the samples with Hurthle cell predominance, small numbers limit the interpretation of these results. For the GEC, indeterminate thyroid nodules with a predominance of Hurthle cells in their sample appear to have an increased rate of “suspicious” results when compared to samples without significant Hurthle cells. The ROM for these nodules on surgical resection, however, is lower, suggesting that there may be an increase in false-positive GEC in Hurthle cell lesions.
Table 1
Abstracts categories of the thyroid system. The risk of malignancy in a thyroid lesion categorized as AUS is 5%-15%. The goal of our study is to assess the outcome of AUS at our institution. Materials and Methods: We reviewed six years of our archives (Jan 2010 December 2016). All thyroid fine needle aspirations with the diagnosis of AUS were selected. Their results on resection were reviewed. Results: Out of a total of 1,987 thyroid FNAs that were performed, 120 were diagnosed as AUS (6%). Only 53 AUS cases (44%) underwent a resection procedure, and 66 were lost to follow-up / did not undergo surgery. Of the 53 resection specimens, 12 were diagnosed with malignancy (22%). Seven patients had benign diagnoses on repeat FNA. One patient died. (Table). Conclusion: Although our AUS diagnosis rate is low (6%), our rate of malignant diagnosis on resection specimen for these cases is 22%, which is above the estimated risk of malignancy according to the Bethesda system.
PST166 Hurthle Cell Predominance Impacts Results of GEC and Molecular Panel Performance in Indeterminate Thyroid Nodules Shobha Parajuli, MD, Rachel Jug, MD, Sara Ahmadi, MD, Xiaoyin Jiang, MD. Duke University Medical Center, Durham, NC Introduction: Molecular tests such as the Afirma Gene Expression Classifier (GEC) and mutational panels (such as Thyroseq) have been introduced to help risk stratify the cytologically-indeterminate thyroid nodule, with the aim to reduce the number of unnecessary thyroidectomies. Some reports have suggested that samples with Hurthle cell predominance may have a higher false-positive rate on GEC testing, but the data are limited, and little is known about the impact of Hurthle cells on molecular panel performance. Materials and Methods: We reviewed indeterminate (Bethesda III/IV) thyroid nodules from June 2012 through August 2016. Patient demographics, cytology diagnosis, presence of Hurthle cells, molecular test results, and histopathologic diagnosis were collected. Patients who had no result or whose result indicated parathyroid tissue were excluded. Results: The Afirma GEC was performed on 208 patients and ThyroSeq was performed on 96 patients. In the GEC cohort (Table 1), 66% of nodules with Hurthle cells yielded a “suspicious result” versus 47% of nodules without significant Hurthle cells, with a risk of malignancy (ROM) of 18% and 35%, respectively. In the Thyroseq cohort (Table 2), 11% of nodules with Hurthle cells yielded a high risk mutation versus 20% of nodules without significant Hurthle cells, with a ROM of 50% and 7%, respectively. Conclusions: For the molecular panel, while it did not appear that there was an increase in the rate of high-risk mutations being detected in the samples with Hurthle cell predominance, small numbers limit the interpretation of these results. For the GEC, indeterminate thyroid nodules with a predominance of Hurthle cells in their sample appear to have an increased rate of “suspicious” results when compared to samples without significant Hurthle cells. The ROM for these nodules on surgical resection, however, is lower, suggesting that there may be an increase in false-positive GEC in Hurthle cell lesions.
Table 1