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: A phase II study of thalidomide in advanced metastatic renal cell carcinoma .
### Output Text:
A phase II study of <span class="chemical">thalidomide</span> in advanced metastatic renal cell carcinoma . 