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: Four of 44 patients ( 9 % ) evaluable for response exhibited objective and subjective evidence of an antineoplastic effect of therapy .
### Output Text:
Four of 44 patients ( 9 % ) evaluable for response exhibited objective and subjective evidence of an antineoplastic effect of therapy . 