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: The results demonstrated that 17beta - estradiol ( E2 ) induces neovascularization , as well as the growth and enlargement of blood vessels after 7 days of exposure .
### Output Text:
The results demonstrated that <span class="chemical">17beta - estradiol</span> ( <span class="chemical">E2</span> ) induces neovascularization , as well as the growth and enlargement of blood vessels after 7 days of exposure . 