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 who had endometrial cancer and had received tamoxifen had more advanced disease and poorer prognosis than those with endometrial cancer who had not received this treatment .
### Output Text:
Women who had endometrial cancer and had received <span class="chemical">tamoxifen</span> had more advanced disease and poorer prognosis than those with endometrial cancer who had not received this treatment . 