In the sentence extracted from biomedical literature, identify all the chemical entities. The required answer format is the same sentence with HTML <span> tags to mark up specific entities. 
### Entity Markup Guides:
Use <span class="chemical"> to denote a chemical.

### Input Text: In six of eight patients ( 75 % ) who we treated for recurrent or resistant glioma , sudden severe neurologic deterioration occurred .
### Output Text:
In six of eight patients ( 75 % ) who we treated for recurrent or resistant glioma , sudden severe neurologic deterioration occurred . 