Is the PIK3CA gene expression level in FNAB washouts equivalent to that in postoperative tissue specimens of papillary thyroid carcinoma?

INTRODUCTION: Papillary thyroid carcinoma (PTC) is the most common malignant tumor of the thyroid gland. The pathogenesis of PTC remains still mostly enigmatic, although PI3K/PTEN/AKT pathway has been proposed to play a role in development of PTC. Moreover, the significance of genetic analysis in the material from fine-needle aspiration biopsy (FNAB) in PTC patients has recently been demonstrated. Hereby, we present a study analyzing expression of PIK3CA in FNAB washouts of PTC and a comparison of the level of that expression with respective expression in postoperative PTC tissue. Furthermore, we have assessed correlation between tumor size, evaluated according to pTNM scale, and level of PIK3CA gene expression in postoperative PTC tissue.

METHODS: Total RNA was extracted by use of an RNeasy Micro Kit (Qiagen, Hilden, Germany) in FNAB material, and RNeasy Midi Kit (Qiagen, Hilden, Germany) in tissue material. The purity of total RNA was assessed by NanoDrop® ND-100 spectrophotometr. One hundred nanograms of total RNA were used in the first strand cDNA synthesis with TaqMan® Reverse Transcripton Reagents (Applied Biosystems, Branchburg, New Jersey, USA). The gene expression level of PIK3CA was analyzed by real-time PCR in the ABI PRISM ®7500 Sequence Detection System in the 21 (17 women, 4 men) FNAB and 20 (16 women, 4 men) postsurgical specimens of PTC. pTNM staging of PTC was assessed based on UICC classification.

RESULTS: Overexpression of PIK3CA was confirmed in FNAB washout specimens and in postoperative tissues of PTC, in comparison to macroscopically unchanged thyroid tissue. Furthermore, statistically significant differences in PIK3CA gene expression levels between both examined groups were not confirmed. Moreover, correlation between pTNM staging and level of PIK3CA gene expression in PTC samples was not found.

CONCLUSION: The genetic analysis of overexpression of PIK3CA in FNAB washout specimens may be equivalent of postsurgical PTC tissue. A possibility of its future clinical application in FNAB specimens - adequate or undetermined for cytological analysis - awaits for evaluation. The level of expression of PIK3CA is independent of primary thyroid tumour size, evaluated according pTNM scale.