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: A 61 - year - old Japanese man with nephrotic syndrome due to focal segmental glomerulosclerosis was initially responding well to steroid therapy .
### Output Text:
A 61 - year - old Japanese man with nephrotic syndrome due to focal segmental glomerulosclerosis was initially responding well to <span class="chemical">steroid</span> therapy . 