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: Data on the possible increased risk of malignancy in rheumatoid arthritis are still being collected , and until further information is available , the use of immunosuppressive drugs , particularly alkylating agents , in the treatment of rheumatoid arthritis should be reserved for patients with severe progressive disease or life - threatening complications .
### Output Text:
Data on the possible increased risk of malignancy in rheumatoid arthritis are still being collected , and until further information is available , the use of immunosuppressive drugs , particularly <span class="chemical">alkylating agents</span> , in the treatment of rheumatoid arthritis should be reserved for patients with severe progressive disease or life - threatening complications . 