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: Urinary protein excretion was unaltered by rhIGF - I treatment in rats with chronic PAN nephropathy .
### Output Text:
Urinary protein excretion was unaltered by rhIGF - I treatment in rats with chronic <span class="chemical">PAN</span> nephropathy . 