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: Paclitaxel , 5 - fluorouracil , and folinic acid in metastatic breast cancer : BRE - 26 , a phase II trial .
### Output Text:
<span class="chemical">Paclitaxel</span> , <span class="chemical">5 - fluorouracil</span> , and <span class="chemical">folinic acid</span> in metastatic breast cancer : BRE - 26 , a phase II trial . 