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: Twenty - six had minimal prior therapy ( good risk ) , 23 had extensive prior therapy ( poor risk ) , and six had renal and / or hepatic dysfunction .
### Output Text:
Twenty - six had minimal prior therapy ( good risk ) , 23 had extensive prior therapy ( poor risk ) , and six had renal and / or hepatic dysfunction . 