MON-570 Clinical Utility of ThyroSeq v3 Genomic Classifier Test in Detecting Gene Fusions in Thyroid Nodules

Yield and costs of molecular diagnostics on thyroid cytology slides in the Netherlands, adapting the Bethesda classification

Objective

To evaluate our institutional experience with molecular diagnostics (MD) on thyroid cytology smears, evaluate the costs and describe MD guided clinical management of indeterminate Bethesda III/V thyroid nodules.

Methods

We performed a retrospective review of 164 Bethesda III or V thyroid cytopathology reports subjected to MD from 2013 to 2020, that altered Bethesda classification or management. MD consisted of mutation and gene fusion analysis by next‐generation sequencing (NGS) of morphologically analysed and selected cytological slides. Findings were modelled to nationwide data on Bethesda incidences from ‘the Dutch Pathology Registry’ PALGA, and costs were estimated.

Results

82 of 164 cases received an upgrade in Bethesda class. Twenty cases changed from Bethesda III to IV/V, 62 from Bethesda III or V to VI, and 72 remained unaltered. We estimate net savings with implementing MD, by preventing 454 repeat cytology and 326 (diagnostic) hemithyroidectomies, to be at least 2 million Euro annually in the Netherlands. Per Bethesda III and V patient, net savings would be about 100 Euro and 4100 Euro, respectively.

Conclusion

NGS‐based MD on nucleic acids extracted directly from cytology slides is a feasible and cost saving tool for personalized management in indeterminate Bethesda III/V thyroid cytology. Based on the interpretation of our retrospective data, we assume that this approach results in less disease burden for the patient, reduced surgical interventions and complication risks, reduced sick leave, among others. Further evaluation of structural implementation of the presented approach in routine thyroid Bethesda III/V cytology in a prospective setting is warranted.

The Role of the ThyroSeq v3 Molecular Test in the Surgical Management of Thyroid Nodules in the Canadian Public Health Care Setting

Background: Although the current gold standard for diagnosing thyroid nodule malignancy is ultrasound-guided fine-needle aspiration (FNA) cytology, about 20-25% of cytological evaluations are considered indeterminate for malignancy. This limitation has led to the emergence of next-generation sequencing panels, for example, ThyroSeq v3 (TSv3), which recognize highly diagnostic genetic mutations of common thyroid carcinomas in FNA samples and classify them as test-negative or test-positive, helping optimize treatment for indeterminate thyroid nodules (ITNs). Our goals were to evaluate the benign call rate (BCR) of TSv3 and assess its diagnostic performance and clinical utility while highlighting the points of consideration for a public Canadian institution. Methods: This is a single-center study conducted at the Royal Victoria Hospital (McGill University Health Centre) in Montreal, Canada, between January and February 2019. Patients were offered TSv3 following the McGill algorithm for ITN workup, a novel protocol developed at our institution to select only diagnostic surgery candidates to minimize waste of public resources, considering the single-payer health care system. Patient demographics, cytopathology results, TSv3 data, treatment plan, and final histopathology result were reviewed. Results: A total of 50 ITNs underwent TSv3 testing; molecular analysis yielded 20 (40%) "positive" results and 24 (48%) "negative" results. Six (12%) results were classified as "currently negative" or "negative but limited." "Currently negative" results indicate a low-risk mutation that alone is insufficient for development of a malignant lesion. "Negative but limited" results indicate a sample that is nondiagnostic for malignancy due to low cell count. BCR was calculated as ("negative" and "currently negative")/total, resulting in a BCR of 58%. Twenty-three (46%) patients were scheduled for surgery and 27 (54%) patients continued with surveillance. Ninety-one percent (20 of 22) of the resected target nodules were malignant on final pathology. Conclusions: TSv3 proved beneficial in classifying ITNs as positive or negative, avoiding surgery in the latter cases. We found a lower reduction rate in surgery and BCR than the previously published studies, which is attributable to the criteria of the McGill algorithm. In the Canadian public health care system, preventing unnecessary surgery represents significant cost savings for the provincial government while also improving patient quality of life.