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: Paclitaxel / cisplatin is an effective first - line regimen for locoregionally advanced head and neck cancer and continued study is warranted .
### Output Text:
<span class="chemical">Paclitaxel</span> / <span class="chemical">cisplatin</span> is an effective first - line regimen for locoregionally advanced head and neck cancer and continued study is warranted . 