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: Bort - dex was an effective salvage treatment for MM patients , particularly for those in first relapse .
### Output Text:
<span class="chemical">Bort</span> - <span class="chemical">dex</span> was an effective salvage treatment for MM patients , particularly for those in first relapse . 