20203
Methods : We now explored if post - radiotherapy and post - Chernobyl thyroid papillary carcinomas ( PTC ) display common molecular features by comparing molecular pathways deregulated in the two tumor series and test the potential of gene subsets of the post - radiotherapy signature to classify the post - Chernobyl series ( 14 sporadic and 12 post - Chernobyl PTC ) , and reciprocally of gene subsets of the post - Chernobyl signature to classify the post - radiotherapy series ( 15 sporadic and 12 post - radiotherapy PTC ) , by using conventional Principal Component Analysis .
 None
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
 None