3995
At 18 months , lung tumors were found to be enhanced concentration dependently ( up to threefold beyond sham exposure ) , irrespective of whether MS inhalation had been performed for the complete study duration or was interrupted after 5 or 10 months and followed by postinhalation periods .
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Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Chemical 
Text: {0} 
Answer:
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