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: Overall response rate ( ORR ) to GEM - P in the entire cohort was 80 % ( complete response ( CR ) 37 % , partial response 44 % ) with 14 / 15 CR confirmed as a metabolic CR on PET and ORR of 85 % in the 20 second - line patients .
### Output Text:
Overall response rate ( ORR ) to <span class="chemical">GEM</span> - P in the entire cohort was 80 % ( complete response ( CR ) 37 % , partial response 44 % ) with 14 / 15 CR confirmed as a metabolic CR on PET and ORR of 85 % in the 20 second - line patients . 