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: MATERIALS AND METHODS : The medical records of 6 men and 6 women ( mean age 55 years ) with cyclophosphamide associated bladder cancer were reviewed .
### Output Text:
MATERIALS AND METHODS : The medical records of 6 men and 6 women ( mean age 55 years ) with <span class="chemical">cyclophosphamide</span> associated bladder cancer were reviewed . 