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: Dobutamine stress echocardiography : a sensitive indicator of diminished myocardial function in asymptomatic doxorubicin - treated long - term survivors of childhood cancer .
### Output Text:
<span class="chemical">Dobutamine</span> stress echocardiography : a sensitive indicator of diminished myocardial function in asymptomatic <span class="chemical">doxorubicin</span> - treated long - term survivors of childhood cancer . 