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: Median cumulative doxorubicin dose at onset was more than 2 , 220 mg / m ( 2 ) for MC versus 480 mg / m ( 2 ) for AC ( P = . 0001 , hazard ratio , 5 . 04 ) .
### Output Text:
Median cumulative <span class="chemical">doxorubicin</span> dose at onset was more than 2 , 220 mg / m ( 2 ) for MC versus 480 mg / m ( 2 ) for AC ( P = . 0001 , hazard ratio , 5 . 04 ) . 