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: Lenalidomide and dexamethasone ( RD ) is a standard of care for relapsed / refractory multiple myeloma ( RRMM ) , but there is limited published data on its efficacy and safety in the " real world " ( RW ) , according to the International Society of Pharmacoeconomics and Outcomes Research definition .
### Output Text:
<span class="chemical">Lenalidomide</span> and <span class="chemical">dexamethasone</span> ( <span class="chemical">RD</span> ) is a standard of care for relapsed / refractory multiple myeloma ( RRMM ) , but there is limited published data on its efficacy and safety in the " real world " ( RW ) , according to the International Society of Pharmacoeconomics and Outcomes Research definition . 