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: In order to quantify the incidence of these cardiac events , we performed a meta - analysis of clinical trials comparing VNR with other chemotherapeutic agents in the treatment of various malignancies .
### Output Text:
In order to quantify the incidence of these cardiac events , we performed a meta - analysis of clinical trials comparing <span class="chemical">VNR</span> with other chemotherapeutic agents in the treatment of various malignancies . 