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 glomerulosclerosis index ( GSI ) was 6 . 21 % at 4 weeks and respectively 25 . 35 % and 30 . 49 % at 14 and 20 weeks in the PAN group .
### Output Text:
The glomerulosclerosis index ( GSI ) was 6 . 21 % at 4 weeks and respectively 25 . 35 % and 30 . 49 % at 14 and 20 weeks in the <span class="chemical">PAN</span> group . 