We investigated protein abundance in order to differentiate radiation-associated papillary thyroid cancers (PTC) from other etiologies for e.g. forensic purposes. Proteins were extracted from frozen tissues originating from 91 sporadic PTCs and 86 post-Chernobyl PTCs. Proteins were separated gel-electrophoretically, gels were silver stained, spots scanned and their intensity quantified. After excision of spots from the gel and protein digestion, MALDI-TOF mass spectrometry was performed followed by correlation of these results to human proteins using appropriate software and database. After this screening approach, altogether 20 candidate proteins were selected and measured semiquantitatively (Remmele score) using immunohistochemistry. Logistic regression modeling was performed for discriminating the groups. NTRK1, metalloproteinases (MMP-1, MMP-9 and MMP-13) and Cathepsins (-W and -X) proved to be of highest significance for discriminating the groups irrespective of the regression model utilized. When considering age and gender, each of 3 proteins by itself made possible a complete separation of the groups otherwise a combination of 2 of the 5 proteins mentioned was needed. In conclusion, abundance of proteins known to be associated with a more aggressive tumor type (MMPs and Cathepsins) appeared increased in post-Chernobyl PTC compared to sporadic PTC, thus underlining the known aggressiveness of radiation-associated PTC. These proteins make it possible to completely distinguish post-Chernobyl from sporadic PTC using routine immunohistology.

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