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: We found that the most - frequent cause of thrombotic microangiopathy was drug related , secondary mainly to cyclosporine .
### Output Text:
We found that the most - frequent cause of thrombotic microangiopathy was drug related , secondary mainly to <span class="chemical">cyclosporine</span> . 