Introduction: Standard pre-operative diagnosis of nodular goitre is not always conclusive. The decision about nodular goitre surgery is increasingly based on molecular methods. The aim of the study was to determine BRAF T1799A mutation and KRas proto-oncogene mutation, and the analysis of RASSF1A promoter methylation level in cytological material obtained from FNAB specimens of thyroid nodules.

Material and methods: The study population consisted of 85 women and 12 men. The study material was genomic DNA isolated from peripheral blood and thyroid bioptates. Pyrosequencing was used for the evaluation of RASSF1 methylation level. KRas mutation was investigated with Sanger sequencing. BRAF mutation was analysed by standard methods of real-time amplification detection (real-time PCR) with the use of specific starters surrounding the mutated site.

Results: A significant positive correlation was demonstrated between mean methylation of four CpG islands of RASSF1A gene and thyroid tumour volume and its largest diameter (p < 0.05). KRas mutation was not detected in any of the 97 patients. In 7/85 subjects (8.2%) BRAF mutation was observed. In 6/7 patients with BRAF mutation, FNAB of thyroid nodules confirmed a benign nature of the lesions; the material was non-diagnostic in one patient, and papillary thyroid cancer was diagnosed on the basis of postoperative histopathology assessment.

Conclusions: The results of genetic tests reported in our study indicate that the presence of BRAF mutation or higher RASSF1A methylation levels in FNAB cytology specimens of benign lesions may be useful in the assessment of oncological risk, while the evaluation of KRas proto-oncogene mutation is not a valuable test in pre-operative diagnosis of nodular goitre. (Endokrynol Pol 2015; 66 (5): 384–393)