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: OBJECTIVES : To evaluate the toxicity and activity of thalidomide in patients with advanced metastatic renal cell cancer and to measure changes of one angiogenic factor , vascular endothelial growth factor ( VEGF ) 165 , with therapy .
### Output Text:
OBJECTIVES : To evaluate the toxicity and activity of <span class="chemical">thalidomide</span> in patients with advanced metastatic renal cell cancer and to measure changes of one angiogenic factor , vascular endothelial growth factor ( VEGF ) 165 , with therapy . 