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: CIN developed 4 . 5 - times more frequently in patients with cancer who had undergone recent chemotherapy .
### Output Text:
CIN developed 4 . 5 - times more frequently in patients with cancer who had undergone recent chemotherapy . 