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: Quality of response was independent of previous lines of therapies or previous exposure to thalidomide or bortezomib .
### Output Text:
Quality of response was independent of previous lines of therapies or previous exposure to <span class="chemical">thalidomide</span> or <span class="chemical">bortezomib</span> . 