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: CLINICAL FEATURES : A 50 - year - old woman with low back and right leg pain was scheduled for epidural steroid injection .
### Output Text:
CLINICAL FEATURES : A 50 - year - old woman with low back and right leg pain was scheduled for epidural <span class="chemical">steroid</span> injection . 