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: We report a case of a patient with colon carcinoma and liver metastasis who presented chest pain after 5 - fluorouracil ( 5 - FU ) administration .
### Output Text:
We report a case of a patient with colon carcinoma and liver metastasis who presented chest pain after <span class="chemical">5 - fluorouracil</span> ( <span class="chemical">5 - FU</span> ) administration . 