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: Sixty - seven men with metastatic androgen - independent prostate cancer in an open - label trial of oral thalidomide underwent neurologic examinations and nerve conduction studies ( NCS ) prior to and at 3 - month intervals during treatment .
### Output Text:
Sixty - seven men with metastatic <span class="chemical">androgen</span> - independent prostate cancer in an open - label trial of oral <span class="chemical">thalidomide</span> underwent neurologic examinations and nerve conduction studies ( NCS ) prior to and at 3 - month intervals during treatment . 