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: It has shown promising results alone or in combination with other chemotherapeutic agents in colorectal , breast , pancreaticobiliary , gastric , renal cell and head and neck cancers .
### Output Text:
It has shown promising results alone or in combination with other chemotherapeutic agents in colorectal , breast , pancreaticobiliary , gastric , renal cell and head and neck cancers . 