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: DOX - induced cardiac damage presumably results from the formation of free radicals by DOX .
### Output Text:
<span class="chemical">DOX</span> - induced cardiac damage presumably results from the formation of free radicals by <span class="chemical">DOX</span> . 