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: Prevention of breast cancer with tamoxifen : preliminary findings from the Italian randomised trial among hysterectomised women .
### Output Text:
Prevention of breast cancer with <span class="chemical">tamoxifen</span> : preliminary findings from the Italian randomised trial among hysterectomised women . 