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: The cure rate of infections in cancer patients is adversely affected by neutropenia ( less than 1 , 000 / mm3 ) .
### Output Text:
The cure rate of infections in cancer patients is adversely affected by neutropenia ( less than 1 , 000 / mm3 ) . 