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: CONCLUSIONS : Subtenon carboplatin chemotherapy is associated with significant fibrosis of orbital soft tissues , leading to mechanical restriction of eye movements and making subsequent enucleation difficult .
### Output Text:
CONCLUSIONS : Subtenon <span class="chemical">carboplatin</span> chemotherapy is associated with significant fibrosis of orbital soft tissues , leading to mechanical restriction of eye movements and making subsequent enucleation difficult . 