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: Short - term use of steroid is very effective in ATRA - induced erythema nodosum .
### Output Text:
Short - term use of <span class="chemical">steroid</span> is very effective in <span class="chemical">ATRA</span> - induced erythema nodosum . 