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: Older reports suggest an objective response rate of 8 % when 60 - 120 mg / m2 of cisplatin is administered every 3 - 4 weeks .
### Output Text:
Older reports suggest an objective response rate of 8 % when 60 - 120 mg / m2 of <span class="chemical">cisplatin</span> is administered every 3 - 4 weeks . 