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: Veno - occlusive liver disease after dacarbazine therapy ( DTIC ) for melanoma .
### Output Text:
Veno - occlusive liver disease after <span class="chemical">dacarbazine</span> therapy ( <span class="chemical">DTIC</span> ) for melanoma . 