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: 14 of the 38 patients were previously treated with chemotherapy , 1 with radiation , 6 with both chemotherapy and radiation , and 17 did not have any treatment before CPDD combination .
### Output Text:
14 of the 38 patients were previously treated with chemotherapy , 1 with radiation , 6 with both chemotherapy and radiation , and 17 did not have any treatment before <span class="chemical">CPDD</span> combination . 