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: Compared with the placebo group , there was a significantly increased risk of vascular events and hypertriglyceridaemia among women on tamoxifen .
### Output Text:
Compared with the placebo group , there was a significantly increased risk of vascular events and hypertriglyceridaemia among women on <span class="chemical">tamoxifen</span> . 