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: When used in high doses and in conjunction with autologous bone marrow transplantation , this agent has activity against several treatment - resistant cancers including malignant glioma .
### Output Text:
When used in high doses and in conjunction with autologous bone marrow transplantation , this agent has activity against several treatment - resistant cancers including malignant glioma . 