Detection of the BRAF(V600E) mutation in fine needle aspiration cytology of thyroid papillary microcarcinoma cells selected by manual macrodissection: an easy tool to improve the preoperative diagnosis.

BACKGROUND

Papillary carcinomas with diameters that are less than or equal to 1 cm (thyroid papillary microcarcinoma [mPTC]) are quite common but can carry more risk than previously thought. The proper treatment and management of these lesions is still being debated. Even though fine needle aspiration cytology (FNAC) is considered the best method for the diagnosis of thyroid nodules, its efficacy is still questioned for mPTC. We investigated the role of BRAF gene status in preoperative cytological samples, using manual macrodissection as an additional tool to improve the diagnostic accuracy of mPTC.

METHODS

DNA was extracted directly from stained FNAC smears of 95 patients including 85 with histological diagnoses of papillary thyroid carcinoma (PTC) ≤1 cm and 10 with goiters. The cytological diagnoses of the 95 cases included the following: 42 samples were suspicious for papillary carcinoma, 38 were PTCs, and 15 were indeterminate lesions. DNA was then extracted from the FNAC slides after performing a "manual macrodissection" procedure. The BRAF(V600E) mutational status was determined by sequence analysis in all the patients.

RESULTS

In this study, we showed that the BRAF(V600E) mutation was present with a high frequency in patients with mPTC (74%). The presence of the mutation was independent of the size of the tumor. In our study, the combination of the cytological diagnosis and the molecular analysis was able to identify 82% of all cases of mPTC, with an increase of 37% compared with a morphological diagnosis alone. The morpho-molecular analysis was able to reduce the number of suspicious cases by >70%. All of the goiters had a wild-type BRAF status.

CONCLUSIONS

The analysis of BRAF mutational status in FNAC obtained from papillary microcarcinomas demonstrates that molecular pathology, combined with morphology and molecular biology is a powerful tool for cytological diagnosis of mPTC. Our results also confirm the data supporting the biological relevance of PTCs with diameters that are ≤1 cm and the importance of "manual macrodissection" in the molecular analysis of cytological material.