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: This is the first published report documenting the preferential in vivo binding of estrogen to nuclei of cells in estrogen induced hamster renal carcinomas .
### Output Text:
This is the first published report documenting the preferential in vivo binding of <span class="chemical">estrogen</span> to nuclei of cells in <span class="chemical">estrogen</span> induced hamster renal carcinomas . 