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: We report a case of intractable hemorrhagic cystitis due to cyclophosphamide therapy for Wegener ' s granulomatosis .
### Output Text:
We report a case of intractable hemorrhagic cystitis due to <span class="chemical">cyclophosphamide</span> therapy for Wegener ' s granulomatosis . 