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: Patients who undergo bone marrow transplantation are generally immunosuppressed with a dose of cyclophosphamide ( CYA ) which is usually calculated based on the patient ' s weight .
### Output Text:
Patients who undergo bone marrow transplantation are generally immunosuppressed with a dose of <span class="chemical">cyclophosphamide</span> ( <span class="chemical">CYA</span> ) which is usually calculated based on the patient ' s weight . 