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: Combination chemotherapy with mitoxantrone , high - dose 5 - fluorouracil ( 5 - FU ) and leucovorin ( MFL regimen ) had been reported as an effective and well tolerated regimen .
### Output Text:
Combination chemotherapy with <span class="chemical">mitoxantrone</span> , high - dose <span class="chemical">5 - fluorouracil</span> ( <span class="chemical">5 - FU</span> ) and <span class="chemical">leucovorin</span> ( <span class="chemical">MFL regimen</span> ) had been reported as an effective and well tolerated regimen . 