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: Combination of bortezomib , thalidomide , and dexamethasone ( VTD ) as a consolidation therapy after autologous stem cell transplantation for symptomatic multiple myeloma in Japanese patients .
### Output Text:
Combination of <span class="chemical">bortezomib</span> , <span class="chemical">thalidomide</span> , and <span class="chemical">dexamethasone</span> ( VTD ) as a consolidation therapy after autologous stem cell transplantation for symptomatic multiple myeloma in Japanese patients . 