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 overall patient survival was 88 . 3 % , and 82 . 4 % after 1 and 2 years , respectively .
### Output Text:
The overall patient survival was 88 . 3 % , and 82 . 4 % after 1 and 2 years , respectively . 