7956
Cellular damage from ionizing radiation ( IR ) is in part due to DNA damage and reactive oxygen species , which activate DNA damage response ( DDR ) and cytokine signaling pathways , including the ataxia telangiectasia mutated ( ATM ) and transforming growth factor ( TGF ) beta / Smad pathways .
 oxygen
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Chemical 
Text: {0} 
Answer:
 oxygen