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: The antiangiogenic effects of thalidomide have been assessed in clinical trials in patients with various solid and haematological malignancies .
### Output Text:
The antiangiogenic effects of <span class="chemical">thalidomide</span> have been assessed in clinical trials in patients with various solid and haematological malignancies . 