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: Since mesangial CC clearance from the mesangium did not change during chronic PAN treatment , we conclude that this preferential CC localization within the lesions is caused by an increased CC uptake shortly after injection in apparent vulnerable areas where sclerosis will develop subsequently .
### Output Text:
Since mesangial CC clearance from the mesangium did not change during chronic <span class="chemical">PAN</span> treatment , we conclude that this preferential CC localization within the lesions is caused by an increased CC uptake shortly after injection in apparent vulnerable areas where sclerosis will develop subsequently . 