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: Angiosarcoma of the liver occurred in a 76 - year - old man who had been treated for a well - differentiated adenocarcinoma of the liver with diethylstilbestrol for 13 years .
### Output Text:
Angiosarcoma of the liver occurred in a 76 - year - old man who had been treated for a well - differentiated adenocarcinoma of the liver with <span class="chemical">diethylstilbestrol</span> for 13 years . 