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: Prolonged PFS and OS were observed in patients achieving CR and receiving bort - dex a single line of prior therapy .
### Output Text:
Prolonged PFS and OS were observed in patients achieving CR and receiving <span class="chemical">bort</span> - <span class="chemical">dex</span> a single line of prior therapy . 