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: These results suggest that chemotherapy - induced anemia reduces cytotoxicity of cyclophosphamide in tumors , whereas correction of anemia by rHuEPO treatment ( epoetin alpha ) increases the sensitivity , probably as a result of an improved oxygen supply to tumor tissue .
### Output Text:
These results suggest that chemotherapy - induced anemia reduces cytotoxicity of <span class="chemical">cyclophosphamide</span> in tumors , whereas correction of anemia by rHuEPO treatment ( epoetin alpha ) increases the sensitivity , probably as a result of an improved <span class="chemical">oxygen</span> supply to tumor tissue . 