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: Women using hormone - replacement therapy appear to have benefited from use of tamoxifen .
### Output Text:
Women using hormone - replacement therapy appear to have benefited from use of <span class="chemical">tamoxifen</span> . 