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: STUDY OBJECTIVE : To evaluate the frequency of venous thromboembolism ( VTE ) in patients with advanced androgen - independent prostate cancer who were treated with docetaxel alone or in combination with thalidomide .
### Output Text:
STUDY OBJECTIVE : To evaluate the frequency of venous thromboembolism ( VTE ) in patients with advanced androgen - independent prostate cancer who were treated with <span class="chemical">docetaxel</span> alone or in combination with <span class="chemical">thalidomide</span> . 