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: To date , 30 previously untreated patients , all with a good performance status ( Eastern Cooperative Oncology Group 0 to 2 ) have been entered into this ongoing study .
### Output Text:
To date , 30 previously untreated patients , all with a good performance status ( Eastern Cooperative Oncology Group 0 to 2 ) have been entered into this ongoing study . 