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 report on a combination of everolimus and tacrolimus in 24 patients ( median age , 62 years ) with either myelodysplastic syndrome ( MDS ; n = 17 ) or acute myeloid leukemia ( AML ; n = 7 ) undergoing intensive conditioning followed by HSCT from related ( n = 4 ) or unrelated ( n = 20 ) donors .
### Output Text:
We report on a combination of <span class="chemical">everolimus</span> and <span class="chemical">tacrolimus</span> in 24 patients ( median age , 62 years ) with either myelodysplastic syndrome ( MDS ; n = 17 ) or acute myeloid leukemia ( AML ; n = 7 ) undergoing intensive conditioning followed by HSCT from related ( n = 4 ) or unrelated ( n = 20 ) donors . 