Gene expression profiling shows that, by gene signature, the difference between BRAF-positive and BRAF-negative PTC is so distinct that BRAF-positive cancer may be regarded as a molecular subtype of papillary thyroid cancer (PTC). Since much enthusiasm surrounds the BRAF-oncogene as a molecular prognostic factor, a central focus of our consideration is to weigh the current arguments for and against applying BRAF mutation status of the tumor in clinical practice. The frequency of BRAF mutation in PTC is high-45% on average, with values over 70-80% in some populations. This will mean that implementing BRAF mutation as a factor of poor prognosis will shift many PTC patients, considered up to now as low risk ones, to the more extensive treatment. We estimate that 31% of all PTC patients and 39% of those diagnosed with stage I-II disease will face the risk of overtreatment if the decision will be based on the BRAF-positivity of their tumors. Also, the risk of undertreatment in the young patients with BRAF-negative tumors is evaluated with 26%. We think that, as of now, the evidence-based support for such consequences is still weak. Thus, there is urgent need to look for genes or gene signatures which will be helpful in the stratification of BRAF-positive tumors to specify these with poor prognosis with higher accuracy, needed for clinical decisions. Considering this, in the review we summarize the present status of knowledge on other prognosis-related gene expression changes in papillary and follicular cancer and relate them to he tumor's biology.
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