Detection of RAS mutation by pyrosequencing in thyroid cytology samples

IntroductionFine-needle aspiration cytology (FNAC) is the primary means to distinguish benign from malignant thyroid nodules. However, adjunctive diagnostic tests are needed as 20–40% of FNAC are inconclusive. RAS mutations have been described in differentiated thyroid cancer and they could be used as tumor markers. However, their prevalence varies widely among studies, probably as a result of the detection methods used. We investigated whether the pyrosequencing method can be applied to detect NRAS and KRAS mutations in thyroid aspirates.Patients and methodsA total of 37 thyroid aspirates, including benign hyperplastic nodules (HBN, N = 16) and follicular thyroid carcinomas (FTC, N = 21) were analyzed for the presence of NRAS61 and KRAS13 mutations.ResultsA RAS mutation was found in 31% and 62% of BN and FTC respectively. Most samples displayed a percentage of mutated alleles lower than 50% (median = 30.8% and 15.3% in FTC and HBN respectively), a result compatible with the presence of extra-nodular cells contaminating the FNA or with the subclonal nature of both types of thyroid nodules.DiscussionPyrosequencing is a reliable assay to detect RAS mutations in fine-needle thyroid aspirates.ConclusionsThe low specificity and sensitivity limit the power of this test to distinguish between FTC and benign nodules in inconclusive FNACs.