Evaluation of a Two-Year Routine Application of Molecular Testing of Thyroid Fine-Needle Aspirations Using a Seven-Gene Panel in a Primary Referral Setting in Germany.

Background: Major differences with respect to the diagnostic performance of a "ruling in" approach in the presurgical diagnosis of indeterminate thyroid fine-needle aspirations (FNAs) have been reported. Therefore, the aim of this prospective multicenter study was to investigate the specific diagnostic impact of mutation testing using a seven-gene panel in a routine primary referral setting analyzing FNAs from endocrinology and nuclear medicine practices in Germany.

Methods: RNA and DNA was extracted from 564 routine air-dried FNA smears obtained from 64 physicians and cytologically graded by one experienced cytopathologist. PAX8/PPARG and RET/PTC rearrangements were detected by quantitative polymerase chain reaction, while BRAF and RAS mutations were detected by pyrosequencing. Molecular data were compared to histology and follow-up >1 year, which were available for 322/348 patients undergoing surgery and 33/74 patients having follow-up. Histology results were obtained from the local routine pathologists who were blinded to the molecular test results.

Results: BRAF and RET/PTC mutations were associated with carcinoma in 98% and 100% of samples, respectively. RAS and PAX8/PPARG mutations were associated with carcinoma in 31% and 0% of samples, respectively. Thirty-six percent of the carcinomas were identified by molecular testing in the atypia of undetermined significance/follicular lesion of undetermined significance and follicular neoplasm/suspicious for a follicular neoplasm categories, with malignancy rates of 15% and 17%, respectively. Due to a low percentage of RAS mutation-positive carcinomas in combination with a rather high percentage of RAS mutation-positive benign nodules, the positive predictive values of 41% and 36% in the atypia of undetermined significance/follicular lesion of undetermined significance and follicular neoplasm/suspicious for a follicular neoplasm categories offer only limited diagnostic potential.

Conclusion: In conclusion, the data suggest that the application of the current seven-gene panel in a routine primary referral setting does not improve the presurgical diagnosis of thyroid FNAs. While the diagnostic relevance of RAS mutations in thyroid tumors needs further investigation, more comprehensive mutation panels with more cancer-specific mutations may improve the presurgical diagnosis of thyroid FNAs.