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: She underwent recent chemotherapy with fluorouracil for metastatic colorectal cancer .
### Output Text:
She underwent recent chemotherapy with <span class="chemical">fluorouracil</span> for metastatic colorectal cancer . 