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: Although responding patients were scheduled to receive consolidation radiotherapy and 24 patients received preplanned second - line chemotherapy after disease progression , the response and toxicity rates reported refer only to the chemotherapy regimen given .
### Output Text:
Although responding patients were scheduled to receive consolidation radiotherapy and 24 patients received preplanned second - line chemotherapy after disease progression , the response and toxicity rates reported refer only to the chemotherapy regimen given . 