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: From October 1993 to November 1995 , we treated 13 patients with previously chemotherapy - treated metastatic breast cancer by mitoxantrone , 12 mg / m2 , on day 1 and continuous infusion of 5 - FU , 3000 mg / m2 , together with leucovorin , 300 mg / m2 , for 48 h from day 1 to 2 .
### Output Text:
From October 1993 to November 1995 , we treated 13 patients with previously chemotherapy - treated metastatic breast cancer by <span class="chemical">mitoxantrone</span> , 12 mg / m2 , on day 1 and continuous infusion of <span class="chemical">5 - FU</span> , 3000 mg / m2 , together with <span class="chemical">leucovorin</span> , 300 mg / m2 , for 48 h from day 1 to 2 . 