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: However , while response and stabilization concerned one - third of the patients , the study did not show increased benefits in terms of survival in patients with unresectable GBM .
### Output Text:
However , while response and stabilization concerned one - third of the patients , the study did not show increased benefits in terms of survival in patients with unresectable GBM . 