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: Bortezomib and dexamethasone as salvage therapy in patients with relapsed / refractory multiple myeloma : analysis of long - term clinical outcomes .
### Output Text:
<span class="chemical">Bortezomib</span> and <span class="chemical">dexamethasone</span> as salvage therapy in patients with relapsed / refractory multiple myeloma : analysis of long - term clinical outcomes . 