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: Graft - versus - host disease prophylaxis with everolimus and tacrolimus is associated with a high incidence of sinusoidal obstruction syndrome and microangiopathy : results of the EVTAC trial .
### Output Text:
Graft - versus - host disease prophylaxis with <span class="chemical">everolimus</span> and <span class="chemical">tacrolimus</span> is associated with a high incidence of sinusoidal obstruction syndrome and microangiopathy : results of the EVTAC trial . 