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: Maximum tolerated dose in good - risk patients was 70 mg / m2 , and in poor - risk patients , 60 mg / m2 .
### Output Text:
Maximum tolerated dose in good - risk patients was 70 mg / m2 , and in poor - risk patients , 60 mg / m2 . 