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: RESULTS : We identified 27 reports of toxic leukoencephalopathy in patients treated with methotrexate ( intrathecal , systemic ) , 5 - fluorouracil and its derivative carmofur , and capecitabine .
### Output Text:
RESULTS : We identified 27 reports of toxic leukoencephalopathy in patients treated with <span class="chemical">methotrexate</span> ( intrathecal , systemic ) , <span class="chemical">5 - fluorouracil</span> and its derivative <span class="chemical">carmofur</span> , and <span class="chemical">capecitabine</span> . 