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: Two cases of clear cell adenocarcinoma of the vagina detected at follow - up in young women exposed in utero to diethylstilbestrol are reported .
### Output Text:
Two cases of clear cell adenocarcinoma of the vagina detected at follow - up in young women exposed in utero to <span class="chemical">diethylstilbestrol</span> are reported . 