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: There is a statistically significant reduction of breast cancer among women receiving tamoxifen who also used hormone - replacement therapy during the trial : among 390 women on such therapy and allocated to placebo , we found eight cases of breast cancer compared with one case among 362 women allocated to tamoxifen .
### Output Text:
There is a statistically significant reduction of breast cancer among women receiving <span class="chemical">tamoxifen</span> who also used hormone - replacement therapy during the trial : among 390 women on such therapy and allocated to placebo , we found eight cases of breast cancer compared with one case among 362 women allocated to <span class="chemical">tamoxifen</span> . 