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: Twenty of 41 ( 48 % ) patients received GEM - P as second - line treatment and 11 / 41 ( 27 % ) as third - line therapy .
### Output Text:
Twenty of 41 ( 48 % ) patients received <span class="chemical">GEM</span> - P as second - line treatment and 11 / 41 ( 27 % ) as third - line therapy . 