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: Although the ability of cyclophosphamide to cause hemorrhagic cystitis and urine cytologic abnormalities indistinguishable from high grade carcinoma is well known , it is less widely appreciated that it is also associated with carcinoma of the urinary tract .
### Output Text:
Although the ability of <span class="chemical">cyclophosphamide</span> to cause hemorrhagic cystitis and urine cytologic abnormalities indistinguishable from high grade carcinoma is well known , it is less widely appreciated that it is also associated with carcinoma of the urinary tract . 