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: We initiated a phase I / II trial to determine the response and toxicity of escalating paclitaxel doses combined with fixed - dose cisplatin with granulocyte colony - stimulating factor support in patients with untreated locally advanced inoperable head and neck carcinoma .
### Output Text:
We initiated a phase I / II trial to determine the response and toxicity of escalating <span class="chemical">paclitaxel</span> doses combined with fixed - dose <span class="chemical">cisplatin</span> with granulocyte colony - stimulating factor support in patients with untreated locally advanced inoperable head and neck carcinoma . 