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: Forty - four MMC - treated patients were studied , 37 of them could be evaluated .
### Output Text:
Forty - four <span class="chemical">MMC</span> - treated patients were studied , 37 of them could be evaluated . 