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: At these high doses of CYA , serious cardiotoxicity may occur , but definitive risk factors for the development of such cardiotoxicity have not been described .
### Output Text:
At these high doses of <span class="chemical">CYA</span> , serious cardiotoxicity may occur , but definitive risk factors for the development of such cardiotoxicity have not been described . 