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: This retrospective study investigated the combination of bort ( 1 . 3 mg / m ( 2 ) on days 1 , 4 , 8 , and 11 every 3 weeks ) and dex ( 20 mg on the day of and the day after bort ) as salvage treatment in 85 patients with R / R MM after prior autologous stem cell transplantation or conventional chemotherapy .
### Output Text:
This retrospective study investigated the combination of <span class="chemical">bort</span> ( 1 . 3 mg / m ( 2 ) on days 1 , 4 , 8 , and 11 every 3 weeks ) and <span class="chemical">dex</span> ( 20 mg on the day of and the day after <span class="chemical">bort</span> ) as salvage treatment in 85 patients with R / R MM after prior autologous stem cell transplantation or conventional chemotherapy . 