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: When tumors were treated with a single dose of cyclophosphamide ( 60 mg / kg i . p . ) 5 days after implantation , a growth delay with a subsequent regrowth of the tumors was observed .
### Output Text:
When tumors were treated with a single dose of <span class="chemical">cyclophosphamide</span> ( 60 mg / kg i . p . ) 5 days after implantation , a growth delay with a subsequent regrowth of the tumors was observed . 