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 most relevant adverse event was peripheral neuropathy , which occurred in 78 % of the patients ( grade II , 38 % ; grade III , 21 % ) and led to treatment discontinuation in 6 % .
### Output Text:
The most relevant adverse event was peripheral neuropathy , which occurred in 78 % of the patients ( grade II , 38 % ; grade III , 21 % ) and led to treatment discontinuation in 6 % . 