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: The similarity between the histologic appearances of busulfan cystitis and both radiation and cyclophosphamide - induced cystitis is discussed and the world literature reviewed .
### Output Text:
The similarity between the histologic appearances of <span class="chemical">busulfan</span> cystitis and both radiation and <span class="chemical">cyclophosphamide</span> - induced cystitis is discussed and the world literature reviewed . 