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: Based on the combined data from the present study and the literature , we suggest that MMC - related cardiotoxicity is dose dependent , occurring at cumulative dose levels of 30 mg m - 2 or more , mainly in patients also ( previously or simultaneously ) treated with doxorubicin .
### Output Text:
Based on the combined data from the present study and the literature , we suggest that <span class="chemical">MMC</span> - related cardiotoxicity is dose dependent , occurring at cumulative dose levels of 30 mg m - 2 or more , mainly in patients also ( previously or simultaneously ) treated with <span class="chemical">doxorubicin</span> . 