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: Data from a Transnational case - control study were used to assess the risk of VTE for the latter patterns of use , while accounting for duration of use .
### Output Text:
Data from a Transnational case - control study were used to assess the risk of VTE for the latter patterns of use , while accounting for duration of use . 